Port better to C23 bool+true+false keywords

Port better to C23 bool+true+false keywords

C23 is adding the C++ keywords bool, true, and false;
prefer them to <stdbool.h> if they are available.
* admin/merge-gnulib (GNULIB_MODULES):
Add stdbool, which emulates C23 on pre-C23 platforms.
(AVOIDED_MODULES): Remove stdbool; Gnulib has renamed
this module to stdbool-c99 and nobody uses it so it does
not need to be avoided.
* m4/c-bool.m4: New file, from Gnulib stdbool module.
* lib-src/seccomp-filter.c, src/conf_post.h, src/dynlib.h:
* src/emacs-module.c, src/nsterm.m, src/systhread.h:
* test/src/emacs-module-resources/mod-test.c:
Use the C23 style and use bool without including <stdbool.h>.
The Gnulib stdbool module causes config.h to include stdbool.h
on pre-C23 platforms.
* src/emacs-module.h.in:
Don’t include <stdbool.h> if C23 or later, or if
it has already been included.