Emacs <config.h> includes <stdlib.h> in some situations, causing
problems on macOS as described by Eli Zaretskii in:
https://lists.gnu.org/r/emacs-devel/2024-12/msg00923.html
Although this usage is not recommended, it is easier to support
it for POSIX-required headers, than to fix Emacs.
* doc/extern-inline.texi (extern inline): Document the Emacs problem.
* lib/endian.c, lib/math.c, lib/stdbit.c, lib/stdlib.c:
* lib/sys_socket.c, lib/unistd.c, lib/wctype-h.c:
Define #define _GL_..._INLINE to _GL_EXTERN_INLINE
before including <config.h>, not merely before including
the .h file that defines the inline function.