Assume C99 or later.

Assume C99 or later.

* lib/stdarg.in.h, lib/stdbool.in.h, m4/stdarg.m4, m4/stdbool.m4:
Remove.
* configure.ac (_AC_PROG_CC_C89): Define a dummy, to keep 'configure'
smaller.
(gl_PROG_CC_C99): Use this to get C99 or later.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
* admin/merge-gnulib (GNULIB_MODULES): Remove stdarg, stdbool.
(GNULIB_TOOL_FLAGS): Avoid stdarg, stdbool.
* doc/lispref/internals.texi (C Dialect): Document this.
* etc/NEWS: Document this.
* nt/gnulib.mk: Remove stdarg and stdbool modules.
* src/bytecode.c (B__dummy__): Remove.
* src/conf_post.h (bool_bf) [!NS_IMPL_GNUSTEP]: Use bool.
(FLEXIBLE_ARRAY_MEMBER): Now always empty.
* src/dbusbind.c (XD_DEBUG_MESSAGE) [!DBUS_DEBUG]:
* src/regex.c (DEBUG_PRINT): Assume varargs macros.
* src/lisp.h (DEFUN_FUNCTION_INIT): Remove.  All uses now assume C99.

Fixes: debbugs:17487