configure: Check for stdio_ext.h

For portability, check for stdio_ext.h during configure and define
HAVE_STDIO_EXT_H accordingly.

If the current system does not provide this header, use a fallback for
__fpending(). This definition will not work on all systems as it relies
on internal data structures of libc. A more portable solution should be
preferred, for example by using gnulib.

configure.ac

@@ -137,6 +137,8 @@ dnl else
 dnl	ALL_LINGUAS="af am ar as be bg bn_IN bn ca cs cy da de el en_GB es et eu_ES fa fi fr gl gu he hi hr hu hy id is it ja ka kn ko ku lo lt lv mk ml mr ms my nb nl nn no nso or pa pl pt_BR pt ro ru si sk sl sq sr@Latn sr sv ta te th tr uk ur vi zh_CN zh_TW zu"
 dnl fi
 
+AC_CHECK_HEADERS(stdio_ext.h, [], [], AC_INCLUDES_DEFAULT)
+
 AC_MSG_CHECKING(whether program_invocation_name is defined)
 AC_TRY_COMPILE([#include <errno.h>],
 		[program_invocation_name = "test";],

lib/fileutils.c

@@ -1,6 +1,12 @@
 #include <errno.h>
 #include <error.h>
-#include <stdio_ext.h>
+#ifdef HAVE_STDIO_EXT_H
+# include <stdio_ext.h>
+#else
+/* FIXME: use a more portable definition of __fpending() (from gnulib?) */
+# include <stdio.h>
+# define __fpending(fp) ((fp)->_p - (fp)->_bf._base)
+#endif
 #include <stdlib.h>
 #include <unistd.h>