Be more systematic about putting space before paren in calls,
and in avoiding unnecessary parentheses in macros.
This was partly inspired by my wading through gcc -E output
while debugging something else, and seeing too many parens.

This patch does not change the generated .o files on my platform.

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.

mod-test.c should not use Gnulib code, as that creates
unnecessary coupling between Emacs internals and this test module.
Also Gnulib code is compiled without -fPIC whereas mod-test.c
needs -fPIC and recompiling Gnulib with -fPIC would be too painful.
* src/Makefile.in (LIB_NANOSLEEP): New macro.
(LIBES): Use it.
* test/Makefile.in (REPLACE_FREE, FREE_SOURCE_0, FREE_SOURCE_0):
Remove.  All uses removed.
(LIB_CLOCK_GETTIME, LIB_NANOSLEEP): New macros.
(MODULE_CFLAGS): Do not -I from lib as that would include Gnulib
modifications to standard .h files (e.g., "#define nanosleep
rpl_nanosleep") and we don’t want the Gnulib replacements.
Instead, for gmp.h (on platforms lacking <gmp.h>) simply '-I.'
with a suitable gmp.h.
(gmp.h): New rule to create a suitable gmp.h.
($(test_module)): Depend on config.h since the code uses config.h.
Depend on gmp.h if we need to create a suitable one.
If compiling mini-gmp.h, compile the original one and not
the Emacs-specific one, to lessen coupling with Emacs internals.
Link with LIB_CLOCK_GETTIME and LIB_NANOSLEEP.
(clean): Remove gmp.h.
* test/src/emacs-module-resources/mod-test.c: Don’t include timespec.h.
All uses of timespec.h APIs changed to use system-supplied APIs.
Change _Static_assert to plain assert, so that we needn’t rely
on Gnulib’s _Static_assert.
(timespec_le) [CLOCK_REALTIME]: New function.
Change use of timespec_cmp changed to use this instead.
(Fmod_test_sleep_until, Fmod_test_nanoseconds):
Define these functions and their Lisp names mod-test-sleep-until
and mod-test-nanoseconds only if CLOCK_REALTIME,
since they now won’t work on platforms lacking CLOCK_REALTIME.
(Fmod_test_nanoseconds): Just use _Static_assert since it
should work on all platforms.
* test/src/emacs-module-tests.el (mod-test-sleep-until)
(mod-test-nanoseconds, mod-test-double):
Skip test if the corresponding functione is not defined.

* test/src/emacs-module-resources/mod-test.c (Fmod_test_userptr_make):
Don’t dump core if calloc returns null and signal_errno returns.

* oldXMenu/Create.c (XMenuCreate):
* oldXMenu/Internal.c (_XMRecomputePane, _XMRecomputeSelection):
* oldXMenu/XMakeAssoc.c (XMakeAssoc):
* test/src/emacs-module-resources/mod-test.c (Fmod_test_userptr_make):
Don’t assume that malloc and calloc succeed.

Run "TZ=UTC0 admin/update-copyright".

When creating multibyte or unibyte strings, we should guarantee the
following invariants:

- When creating empty strings, a NULL data pointer should be allowed.
  This often arises in practice if the string length isn't known in
  advance, and we don't want to unnecessarily trigger undefined
  behavior.  Since functions like memcpy might not accept NULL
  pointers, use the canonical empty string objects in this case.

- Nonzero strings should be guaranteed to be unique and mutable.
  These are the same guarantees expected from Lisp functions such as
  'make-string' or 'unibyte-string'.  On the other hand, empty strings
  might not be unique.

* src/emacs-module.c (module_make_string)
(module_make_unibyte_string): Correctly handle empty strings.

* test/src/emacs-module-resources/mod-test.c (Fmod_test_make_string):
New test function.
(emacs_module_init): Expose it.

* test/src/emacs-module-tests.el (mod-test-make-string/empty)
(mod-test-make-string/nonempty): New unit tests.

* doc/lispref/internals.texi (Module Values): Document properties and
corner cases for strings.