autoconf: Use ":" instead of "dnl" as a noop

[real-or-random]

Fixes #424.

[elichai]

Testing setup: (output: https://pastebin.com/raw/LC8ZLCgj)

$ docker run -ti centos:6.7 /bin/bash
$ yum install -y http://opensource.wandisco.com/centos/6/git/x86_64/wandisco-git-release-6-1.noarch.rpm
$ yum install -y git autoconf automake openssl ca-certificates nss curl libtool tar
$ git clone https://github.com/bitcoin-core/secp256k1.git
$ cd secp256k1

Before:

$ ./autogen.sh
libtoolize: putting auxiliary files in AC_CONFIG_AUX_DIR, `build-aux'.
libtoolize: copying file `build-aux/ltmain.sh'
libtoolize: putting macros in AC_CONFIG_MACRO_DIR, `build-aux/m4'.
libtoolize: copying file `build-aux/m4/libtool.m4'
libtoolize: copying file `build-aux/m4/ltoptions.m4'
libtoolize: copying file `build-aux/m4/ltsugar.m4'
libtoolize: copying file `build-aux/m4/ltversion.m4'
libtoolize: copying file `build-aux/m4/lt~obsolete.m4'
configure.ac:27: installing `build-aux/compile'
configure.ac:5: installing `build-aux/config.guess'
configure.ac:5: installing `build-aux/config.sub'
configure.ac:9: installing `build-aux/install-sh'
configure.ac:9: installing `build-aux/missing'
Makefile.am: installing `build-aux/depcomp'

$ ./configure
checking build system type... x86_64-unknown-linux-gnu
checking host system type... x86_64-unknown-linux-gnu
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking for style of include used by make... GNU
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables... 
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking dependency style of gcc... gcc3
checking for a sed that does not truncate output... /bin/sed
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking for fgrep... /bin/grep -F
checking for ld used by gcc... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for BSD- or MS-compatible name lister (nm)... /usr/bin/nm -B
checking the name lister (/usr/bin/nm -B) interface... BSD nm
checking whether ln -s works... yes
checking the maximum length of command line arguments... 1572864
checking whether the shell understands some XSI constructs... yes
checking whether the shell understands "+="... yes
checking for /usr/bin/ld option to reload object files... -r
checking for objdump... objdump
checking how to recognize dependent libraries... pass_all
checking for ar... ar
checking for strip... strip
checking for ranlib... ranlib
checking command to parse /usr/bin/nm -B output from gcc object... ok
./configure: line 5754: /usr/bin/file: No such file or directory
checking how to run the C preprocessor... gcc -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking for dlfcn.h... yes
checking for objdir... .libs
checking if gcc supports -fno-rtti -fno-exceptions... no
checking for gcc option to produce PIC... -fPIC -DPIC
checking if gcc PIC flag -fPIC -DPIC works... yes
checking if gcc static flag -static works... no
checking if gcc supports -c -o file.o... yes
checking if gcc supports -c -o file.o... (cached) yes
checking whether the gcc linker (/usr/bin/ld) supports shared libraries... yes
checking whether -lc should be explicitly linked in... no
checking dynamic linker characteristics... GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... yes
checking for pkg-config... /usr/bin/pkg-config
checking pkg-config is at least version 0.9.0... yes
checking for ar... /usr/bin/ar
checking for ranlib... /usr/bin/ranlib
checking for strip... /usr/bin/strip
checking for gcc... gcc
checking whether we are using the GNU C compiler... (cached) yes
checking whether gcc accepts -g... no
checking for gcc option to accept ISO C89... (cached) none needed
checking dependency style of gcc... gcc3
checking how to run the C preprocessor... gcc -E
checking whether gcc and cc understand -c and -o together... yes
checking for gcc option to accept ISO C89... (cached) none needed
checking dependency style of gcc... gcc3
checking if gcc supports -std=c89 -pedantic -Wall -Wextra -Wcast-align -Wnested-externs -Wshadow -Wstrict-prototypes -Wno-unused-function -Wno-long-long -Wno-overlength-strings... yes
checking if gcc supports -fvisibility=hidden... yes
checking for __int128... no
checking valgrind/memcheck.h usability... no
checking valgrind/memcheck.h presence... no
checking for valgrind/memcheck.h... no
./configure: line 13726: syntax error near unexpected token `else'
./configure: line 13726: `  else'

After:

$ git pull origin refs/pull/752/head
$ git checkout FETCH_HEAD
$ ./autogen.sh
libtoolize: putting auxiliary files in AC_CONFIG_AUX_DIR, `build-aux'.
libtoolize: copying file `build-aux/ltmain.sh'
libtoolize: putting macros in AC_CONFIG_MACRO_DIR, `build-aux/m4'.
libtoolize: copying file `build-aux/m4/libtool.m4'
libtoolize: copying file `build-aux/m4/ltoptions.m4'
libtoolize: copying file `build-aux/m4/ltsugar.m4'
libtoolize: copying file `build-aux/m4/ltversion.m4'
libtoolize: copying file `build-aux/m4/lt~obsolete.m4'
$ ./configure 
checking build system type... x86_64-unknown-linux-gnu
checking host system type... x86_64-unknown-linux-gnu
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking for style of include used by make... GNU
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables... 
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking dependency style of gcc... gcc3
checking for a sed that does not truncate output... /bin/sed
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking for fgrep... /bin/grep -F
checking for ld used by gcc... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for BSD- or MS-compatible name lister (nm)... /usr/bin/nm -B
checking the name lister (/usr/bin/nm -B) interface... BSD nm
checking whether ln -s works... yes
checking the maximum length of command line arguments... 1572864
checking whether the shell understands some XSI constructs... yes
checking whether the shell understands "+="... yes
checking for /usr/bin/ld option to reload object files... -r
checking for objdump... objdump
checking how to recognize dependent libraries... pass_all
checking for ar... ar
checking for strip... strip
checking for ranlib... ranlib
checking command to parse /usr/bin/nm -B output from gcc object... ok
./configure: line 5754: /usr/bin/file: No such file or directory
checking how to run the C preprocessor... gcc -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking for dlfcn.h... yes
checking for objdir... .libs
checking if gcc supports -fno-rtti -fno-exceptions... no
checking for gcc option to produce PIC... -fPIC -DPIC
checking if gcc PIC flag -fPIC -DPIC works... yes
checking if gcc static flag -static works... no
checking if gcc supports -c -o file.o... yes
checking if gcc supports -c -o file.o... (cached) yes
checking whether the gcc linker (/usr/bin/ld) supports shared libraries... yes
checking whether -lc should be explicitly linked in... no
checking dynamic linker characteristics... GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... yes
checking for pkg-config... /usr/bin/pkg-config
checking pkg-config is at least version 0.9.0... yes
checking for ar... /usr/bin/ar
checking for ranlib... /usr/bin/ranlib
checking for strip... /usr/bin/strip
checking for gcc... gcc
checking whether we are using the GNU C compiler... (cached) yes
checking whether gcc accepts -g... no
checking for gcc option to accept ISO C89... (cached) none needed
checking dependency style of gcc... gcc3
checking how to run the C preprocessor... gcc -E
checking whether gcc and cc understand -c and -o together... yes
checking for gcc option to accept ISO C89... (cached) none needed
checking dependency style of gcc... gcc3
checking if gcc supports -std=c89 -pedantic -Wall -Wextra -Wcast-align -Wnested-externs -Wshadow -Wstrict-prototypes -Wno-unused-function -Wno-long-long -Wno-overlength-strings... yes
checking if gcc supports -fvisibility=hidden... yes
checking for __int128... no
checking valgrind/memcheck.h usability... no
checking valgrind/memcheck.h presence... no
checking for valgrind/memcheck.h... no
checking if native gcc supports -Wall -Wextra -Wno-unused-function... yes
checking for working native compiler: gcc... yes
checking for x86_64 assembly availability... yes
checking gmp.h usability... no
checking gmp.h presence... no
checking for gmp.h... no
checking for CRYPTO... no
checking openssl/crypto.h usability... no
checking openssl/crypto.h presence... no
checking for openssl/crypto.h... no
checking whether byte ordering is bigendian... no
configure: creating ./config.status
config.status: creating Makefile
config.status: creating libsecp256k1.pc
config.status: creating src/libsecp256k1-config.h
config.status: executing depfiles commands
config.status: executing libtool commands

Build Options:
  with endomorphism       = no
  with ecmult precomp     = yes
  with external callbacks = no
  with benchmarks         = yes
  with coverage           = no
  module ecdh             = no
  module recovery         = no

  asm                     = x86_64
  bignum                  = no
  field                   = 32bit
  scalar                  = 32bit
  ecmult window size      = 15
  ecmult gen prec. bits   = 4

  valgrind                = no
  CC                      = gcc
  CFLAGS                  = -O2 -fvisibility=hidden -std=c89 -pedantic -Wall -Wextra -Wcast-align -Wnested-externs -Wshadow -Wstrict-prototypes -Wno-unused-function -Wno-long-long -Wno-overlength-strings -W -g
  CPPFLAGS                = 
  LDFLAGS                 = 

$ make check
  CC     src/libsecp256k1_la-secp256k1.lo
src/secp256k1.c:78: warning: missing initializer
src/secp256k1.c:78: warning: (near initialization for 'secp256k1_context_no_precomp_.ecmult_gen_ctx.blind')
src/secp256k1.c: In function 'secp256k1_context_preallocated_create':
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.8' does break strict-aliasing rules
src/util.h:125: note: initialized from here
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.8' does break strict-aliasing rules
src/util.h:125: note: initialized from here
  CCLD   libsecp256k1.la
  CC     src/bench_verify-bench_verify.o
  CCLD   bench_verify
  CC     src/bench_sign.o
  CCLD   bench_sign
  CC     src/bench_internal-bench_internal.o
In file included from src/bench_internal.c:19:
src/secp256k1.c:78: warning: missing initializer
src/secp256k1.c:78: warning: (near initialization for 'secp256k1_context_no_precomp_.ecmult_gen_ctx.blind')
src/secp256k1.c: In function 'secp256k1_context_preallocated_create':
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.8' does break strict-aliasing rules
src/util.h:125: note: initialized from here
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.8' does break strict-aliasing rules
src/util.h:125: note: initialized from here
  CCLD   bench_internal
  CC     src/bench_ecmult-bench_ecmult.o
In file included from src/bench_ecmult.c:18:
src/secp256k1.c:78: warning: missing initializer
src/secp256k1.c:78: warning: (near initialization for 'secp256k1_context_no_precomp_.ecmult_gen_ctx.blind')
src/secp256k1.c: In function 'secp256k1_context_preallocated_create':
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.8' does break strict-aliasing rules
src/util.h:125: note: initialized from here
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.8' does break strict-aliasing rules
src/util.h:125: note: initialized from here
  CCLD   bench_ecmult
  CC     src/tests-tests.o
In file included from src/tests.c:17:
src/secp256k1.c:78: warning: missing initializer
src/secp256k1.c:78: warning: (near initialization for 'secp256k1_context_no_precomp_.ecmult_gen_ctx.blind')
src/secp256k1.c: In function 'secp256k1_context_preallocated_create':
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.13' does break strict-aliasing rules
src/util.h:125: note: initialized from here
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.13' does break strict-aliasing rules
src/util.h:125: note: initialized from here
  CCLD   tests
  CC     src/exhaustive_tests-tests_exhaustive.o
In file included from src/tests_exhaustive.c:26:
src/secp256k1.c:78: warning: missing initializer
src/secp256k1.c:78: warning: (near initialization for 'secp256k1_context_no_precomp_.ecmult_gen_ctx.blind')
src/secp256k1.c: In function 'secp256k1_context_preallocated_create':
src/util.h:125: warning: dereferencing pointer 'prealloc_ptr.10' does break strict-aliasing rules
src/util.h:125: note: initialized from here
  CCLD   exhaustive_tests
make  check-TESTS
make[1]: Entering directory `/secp256k1'
test count = 64
random seed = ea96f593d21df6fe83ee2d22763f2a17
random run = c85d052f233e428b6b93dde90c55e11b
no problems found
PASS: tests
PASS: exhaustive_tests
==================
All 2 tests passed
==================
make[1]: Leaving directory `/secp256k1'
make: *** No rule to make target `2'.  Stop.

[elichai]

tACK