Yesterday I did:
> 	* tests/test-vasnwprintf-posix.c (test_function): Add more tests for the
> 	%c and %lc directives.

Some of these new tests fail on musl libc, FreeBSD, NetBSD, AIX, mingw.
- For musl libc, *BSD, AIX, it's a bug in the swprintf function, and as
  a workaround, I'll just not use swprintf on these platforms.
  For musl libc, I have reported it at
  <https://www.openwall.com/lists/musl/2023/03/22/9>.
- For mingw, I'll continue to use the snwprintf function, but with a small
  workaround.


2023-03-22  Bruno Haible  <bruno@clisp.org>

	vasnwprintf: Fix test failures on FreeBSD, NetBSD, AIX, mingw.
	* m4/printf.m4 (gl_SWPRINTF_WORKS): New macro.
	* m4/vasnprintf.m4 (gl_PREREQ_VASNWPRINTF): Invoke it and define
	HAVE_WORKING_SWPRINTF accordingly.
	* lib/vasnprintf.c: Together with HAVE_SWPRINTF, test also
	HAVE_WORKING_SWPRINTF.
	(VASNPRINTF): If WIDE_CHAR_VERSION && !DCHAR_IS_TCHAR, don't pass a
	wchar_t[] to snprintf. Add a workaround against mingw's snwprintf
	function.
	* doc/posix-functions/swprintf.texi: Document the null wide character
	bug.

2023-03-22  Bruno Haible  <bruno@clisp.org>

	vasnwprintf: Fix a "warning: unused function 'wmax_room_needed'".
	* lib/vasnprintf.c (MAX_ROOM_NEEDED): Adjust #if condition.

2023-03-22  Bruno Haible  <bruno@clisp.org>

	vasnwprintf: Simplify last change.
	* lib/vasnprintf.c (VASNPRINTF): Remove unused variable 'len'.