obstack-printf-gnu: New module.

* m4/obstack-printf-posix.m4 (gl_FUNC_OBSTACK_PRINTF_IS_POSIX): New
macro, extracted from gl_FUNC_OBSTACK_PRINTF_POSIX.
(gl_FUNC_OBSTACK_PRINTF_POSIX): Require it. Invoke
gl_PREREQ_VASNPRINTF_WITH_POSIX_EXTRAS.
* m4/obstack-printf-gnu.m4: New file, based on
m4/obstack-printf-posix.m4.
* modules/obstack-printf-gnu: New file, based on modules/vasnprintf-gnu.
* doc/glibc-functions/obstack_printf.texi: Mention the new module.
* doc/glibc-functions/obstack_vprintf.texi: Likewise.

modules/obstack-printf-gnu

@@ -0,0 +1,31 @@
+Description:
+POSIX and GNU compatible formatted printing into an obstack.
+
+Comment:
+This module should not be used as a dependency from a test module,
+otherwise when this module occurs as a tests-related module, it will
+have side effects on the compilation of the 'vasnprintf' module, if
+that module occurs among the main modules in lib/.
+
+Files:
+m4/obstack-printf-gnu.m4
+
+Depends-on:
+obstack-printf-posix
+
+configure.ac:
+gl_FUNC_OBSTACK_PRINTF_GNU
+if test $ac_cv_func_obstack_printf = no || test $REPLACE_OBSTACK_PRINTF = 1; then
+  AC_LIBOBJ([obstack_printf])
+fi
+
+Makefile.am:
+
+Include:
+<stdio.h>
+
+License:
+GPL
+
+Maintainer:
+Eric Blake