build: Remove #undef hack for ASM in the precomputation programs

This was necessary because we used to cross-compile the library but
compile the precomputation programs for the build host. Now it's no
longer necessary and we can cleanly link even the external ASM
(which was the intent of bitcoin#935).

On the way, remove an obsolete "-I" parameter.

Makefile.am

@@ -119,7 +119,7 @@ endif
 if USE_EXHAUSTIVE_TESTS
 noinst_PROGRAMS += exhaustive_tests
 exhaustive_tests_SOURCES = src/tests_exhaustive.c
-exhaustive_tests_CPPFLAGS = -I$(top_srcdir)/src $(SECP_INCLUDES)
+exhaustive_tests_CPPFLAGS = $(SECP_INCLUDES)
 if !ENABLE_COVERAGE
 exhaustive_tests_CPPFLAGS += -DVERIFY
 endif
@@ -131,8 +131,14 @@ endif
 ### Precomputed tables
 EXTRA_PROGRAMS = gen_ecmult_static_pre_g gen_ecmult_gen_static_prec_table
 CLEANFILES = $(EXTRA_PROGRAMS)
+
 gen_ecmult_static_pre_g_SOURCES = src/gen_ecmult_static_pre_g.c
+gen_ecmult_static_pre_g_CPPFLAGS = $(SECP_INCLUDES)
+gen_ecmult_static_pre_g_LDADD = $(SECP_LIBS) $(COMMON_LIB)
+
 gen_ecmult_gen_static_prec_table_SOURCES = src/gen_ecmult_gen_static_prec_table.c
+gen_ecmult_gen_static_prec_table_CPPFLAGS = $(SECP_INCLUDES)
+gen_ecmult_gen_static_prec_table_LDADD = $(SECP_LIBS) $(COMMON_LIB)
 
 # See Automake manual, Section "Errors with distclean".
 # We don't list any dependencies for the prebuilt files here because

src/gen_ecmult_gen_static_prec_table.c

@@ -7,12 +7,6 @@
 #include <inttypes.h>
 #include <stdio.h>
 
-/* In principle we could use ASM, but this yields only a minor speedup in
-   build time and it's very complicated. In particular when cross-compiling, we'd
-   need to build the ASM for the build and the host machine. */
-#undef USE_EXTERNAL_ASM
-#undef USE_ASM_X86_64
-
 #include "../include/secp256k1.h"
 #include "assumptions.h"
 #include "util.h"

src/gen_ecmult_static_pre_g.c

@@ -13,12 +13,6 @@
 #include "libsecp256k1-config.h"
 #endif
 
-/* In principle we could use ASM, but this yields only a minor speedup in
-   build time and it's very complicated. In particular when cross-compiling, we'd
-   need to build the ASM for the build and the host machine. */
-#undef USE_EXTERNAL_ASM
-#undef USE_ASM_X86_64
-
 #include "../include/secp256k1.h"
 #include "assumptions.h"
 #include "util.h"