gmp 6.3.0 fails to configure with gcc 15.2

[StephanTLavavej]

I was able to build gmp 6.3.0 with gcc 13.2, but it fails to configure with gcc 15.2.

This was reported upstream: https://gmplib.org/list-archives/gmp-bugs/2025-December/005607.html

I have a non-intrusive workaround (configure with "CFLAGS=-std=gnu17"); as in #116, the proximate cause appears to be https://gcc.gnu.org/gcc-15/changes.html#c :

C23 by default: GCC 15 changes the default language version for C compilation from -std=gnu17 to -std=gnu23.

As suggested by https://gmplib.org/list-archives/gmp-bugs/2025-December/005608.html , this has already been fixed upstream. From https://gmplib.org/download/snapshot/gmp-next/ , I was able to configure gmp-6.3.0-20250919151842.tar.zst without any workarounds.

[StephanTLavavej]

Fortunately, this doesn't affect gcc's in-tree build of gmp, presumably because they're controlling the C language version or something.