[Mesa-dev] Fix __atomic* builtins detection for Clang

[Jan Beich]

Jan Beich <jbeich at FreeBSD.org> writes:

> "int" isn't large enough and lack of builtins only manifests at link time.
> This was breaking build on FreeBSD 11.0 i386 with Clang 3.8.0.
>
> glsl/.libs/libstandalone.a(libmesautil_la-disk_cache.o): In function `disk_cache_remove':
> disk_cache.c:(.text+0x763): undefined reference to `__atomic_fetch_add_8'
> glsl/.libs/libstandalone.a(libmesautil_la-disk_cache.o): In function `cache_put':
> disk_cache.c:(.text+0xabc): undefined reference to `__atomic_fetch_add_8'
> disk_cache.c:(.text+0xec1): undefined reference to `__atomic_fetch_add_8'
> c++: error: linker command failed with exit code 1 (use -v to see invocation)

v2 is https://lists.freedesktop.org/archives/mesa-dev/2017-May/155499.html