positional parameters: (#79488)
* glib/gstrfuncs.c:
* glib/gspawn-win32.c:
* glib/gscanner.c:
* glib/gconvert.c:
* glib/gbacktrace.c: Use _g_printf wrappers.
* glib/gutils.c (g_vsnprintf): Simplify, since we can assume C99
snprintf semantics now.
* glib/gmessages.c (printf_string_upper_bound): No longer needed,
since we can assume C99 snprintf semantics now.
(g_logv): Simplify.
* acinclude.m4 (AC_FUNC_PRINTF_UNIX98): New macro to check wether
printf supports SUS positional parameters.
* configure.in: New option --enable-included-printf to force
compilation of trio; otherwise trio is compiled if the system
printf misses either C99 snprintf semantics of SUS positional
parameters.
* glib/Makefile.am (SUBDIRS): Conditionally compile trio.
(libglib_2_0_la_SOURCES): Add gprintf.c and gprintfint.h.
(glibsubinclude_HEADERS): Add gprintf.h.
* glib/gprintfint.h: New private wrapping either system printf
or trio printf variants in _g_printf wrappers for use inside glib.
* glib/gprintf.h: New public header declaring g_printf variants.
* glib/gprintf.c: Corresponding implementations.
* glib/trio/*: New directory, containing the trio-1.9 sources.
* glib/tmpl/string_utils.sgml: Add note on including gprintf.h,
move some docs inline.
* glib/glib-sections.txt: Add g_printf, g_vprintf, g_fprintf,
g_vfprintf, g_sprintf, g_vsprintf.
