Fix open_memstream/fmemopen feature detection with GCC >= 14

[nmeum]

GCC 14 has enabled various warnings as errors by default, e.g. -Wimplicit-function-declaration. This causes the current feature detection code for open_memstream(3) and fmemopen(3) to fail with GCC 14.

This commit restores compatibility with GCC 14 in this regard.

Note that it may also be beneficial to pass a feature test macro such as -D_POSIX_C_SOURCE. See the feature test macro requirements for open_memstream(3)andfmemopen(3)`.

See also https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/72328

[justinethier]

Appreciate the report and PR @nmeum!

Unfortunately this change breaks the build:

$ make
Makefile.config:94: *** unterminated call to function 'shell': missing ')'.  Stop.

[nmeum]

Hmmm, what Make implementation are you using? Works for me with GNU make 4.4.1.

Will happily adjust the patch but just can't reproduce this right now.

[justinethier]

Using make 4.2.1 over here:

justin@ubuntu:~/Documents/cyclone/tests$ make --version
GNU Make 4.2.1

That said, this works in my environment:

CYC_PLATFORM_HAS_MEMSTREAM := $(shell echo "\#include \<stdio.h\> int main(void){char *buf; size_t len; open_memstream(&buf, &len);}" | $(CC) -xc - >/dev/null 2>/dev/null && echo 1 || echo 0)
CYC_PLATFORM_HAS_FMEMOPEN := $(shell echo "\#include \<stdio.h\> int main(void){char *buf; fmemopen(&buf, 0, \"r\");}" | $(CC) -xc - >/dev/null 2>/dev/null && echo 1 || echo 0)

[justinethier]

Also, merged in more CI for this repo that will build the C runtime. If you want to repro, you can merge the master branch back into your PR branch and you should see the build failure.

[nmeum]

Ok, I looked into it. This is caused by the following change in GNU Make 4.3:

• WARNING: Backward-incompatibility!
  Number signs (#) appearing inside a macro reference or function invocation
  no longer introduce comments and should not be escaped with backslashes:
  thus a call such as:
  foo := $(shell echo '#')
  is legal. Previously the number sign needed to be escaped, for example:
  foo := $(shell echo '#')
  Now this latter will resolve to "#". If you want to write makefiles
  portable to both versions, assign the number sign to a variable:
  H := #
  foo := $(shell echo '$H')
  This was claimed to be fixed in 3.81, but wasn't, for some reason.
  To detect this change search for 'nocomment' in the .FEATURES variable.

[nmeum]

I added the H := \# hack proposed in that release announcement.

Let me know if that works for you.

[justinethier]

Alright, this works great on my side as well. Appreciate you researching/adding the backwards compatibility and thanks again for the PR!