support GNU format printf and scanf on mingw

Allow %lld and %Lf to work on mingw as per:
http://sourceforge.net/p/mingw-w64/wiki2/gnu%20printf/

m4/extensions.m4

@@ -68,6 +68,10 @@ dnl configure.ac when using autoheader 2.62.
 #ifndef _GNU_SOURCE
 # undef _GNU_SOURCE
 #endif
+/* Use GNU style printf and scanf.  */
+#ifndef __USE_MINGW_ANSI_STDIO
+# undef __USE_MINGW_ANSI_STDIO
+#endif
 /* Enable threading extensions on Solaris.  */
 #ifndef _POSIX_PTHREAD_SEMANTICS
 # undef _POSIX_PTHREAD_SEMANTICS
@@ -100,6 +104,7 @@ dnl configure.ac when using autoheader 2.62.
   AC_DEFINE([_ALL_SOURCE])
   AC_DEFINE([_DARWIN_C_SOURCE])
   AC_DEFINE([_GNU_SOURCE])
+  AC_DEFINE([__USE_MINGW_ANSI_STDIO])
   AC_DEFINE([_POSIX_PTHREAD_SEMANTICS])
   AC_DEFINE([_TANDEM_SOURCE])
   AC_CACHE_CHECK([whether _XOPEN_SOURCE should be defined],

m4/stdio_h.m4

@@ -6,6 +6,9 @@ dnl with or without modifications, as long as this notice is preserved.
 
 AC_DEFUN([gl_STDIO_H],
 [
+  dnl For __USE_MINGW_ANSI_STDIO
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
   AC_REQUIRE([gl_STDIO_H_DEFAULTS])
   gl_NEXT_HEADERS([stdio.h])
 

modules/dtoastr

@@ -8,6 +8,7 @@ lib/dtoastr.c
 m4/c-strtod.m4
 
 Depends-on:
+extensions
 intprops
 
 configure.ac:

modules/ftoastr

@@ -7,6 +7,7 @@ lib/ftoastr.c
 m4/c-strtod.m4
 
 Depends-on:
+extensions
 intprops
 
 configure.ac:

modules/ldtoastr

@@ -8,6 +8,7 @@ lib/ldtoastr.c
 m4/c-strtod.m4
 
 Depends-on:
+extensions
 intprops
 
 configure.ac:

modules/stdio

@@ -6,6 +6,7 @@ lib/stdio.in.h
 m4/stdio_h.m4
 
 Depends-on:
+extensions
 include_next
 snippet/arg-nonnull
 snippet/c++defs