Bug #9555: Always define _GNU_SOURCE in glibc environments.

This keeps us from having to define _POSIX_C_SOURCE, _BSD_SOURCE, and
_XOPEN_SORUCE to get the C environment we want in different places.  It also
fixes the build on linux due to RTLD_DEFAULT having not been defined.
(cherry picked from 7fccec9 commit)

configure.ac

@@ -1599,20 +1599,13 @@ dnl and the rest of these are generic, so they're in config.h
 AC_DEFINE(XFreeXDGA, 1, [Build XDGA support])
 AC_DEFINE(XResExtension, 1, [Build XRes extension])
 
-dnl CYGWIN does not define fd_set if _POSIX_SOURCE is defined
-dnl _*_SOURCE on Solaris restricts to the standards, and removes non-standard
-dnl functions which X uses
-case $host_os in
-	cygwin*) ;;
-	solaris*) ;;
-        darwin*) ;;
-	freebsd*|netbsd*|openbsd*) ;;
-	*) 
-		AC_DEFINE(_POSIX_SOURCE, 1, [POSIX-compliant source])
-		AC_DEFINE(_XOPEN_SOURCE, 500, [X/Open-compliant source])
-		AC_DEFINE(_BSD_SOURCE, 1, [BSD-compliant source])
-		;;
-esac
+AC_TRY_COMPILE([
+#include <features.h>
+#ifndef __GLIBC__
+#error not glibc
+#endif
+], [], [AC_DEFINE(_GNU_SOURCE, 1,
+	[ Enable GNU and other extensions to the C environment for glibc])])
 
 AC_DEFINE_DIR(PROJECTROOT, prefix, [Overall prefix])
 

include/dix-config.h.in

@@ -410,16 +410,8 @@
 /* Endian order */
 #undef X_BYTE_ORDER
 
-/* BSD-compliant source */
-#undef _BSD_SOURCE
-
-/* POSIX-compliant source */
-#undef _POSIX_SOURCE
-
-#ifndef _XOPEN_SOURCE
-/* X/Open-compliant source */
-#undef _XOPEN_SOURCE
-#endif
+/* Enable GNU and other extensions to the C environment for GLIBC */
+#undef _GNU_SOURCE
 
 /* Define to empty if `const' does not conform to ANSI C. */
 #undef const

os/utils.c

@@ -53,23 +53,6 @@ OR PERFORMANCE OF THIS SOFTWARE.
 #include <dix-config.h>
 #endif
 
-/* The world's most shocking hack, to ensure we get clock_gettime() and
- * CLOCK_MONOTONIC. */
-#ifdef sun              /* Needed to tell Solaris headers not to restrict to */
-#define __EXTENSIONS__  /* only the functions defined in POSIX 199309.       */
-#endif
-
-#ifdef _POSIX_C_SOURCE
-#define _SAVED_POSIX_C_SOURCE _POSIX_C_SOURCE
-#undef _POSIX_C_SOURCE
-#endif
-#define _POSIX_C_SOURCE 199309L
-#include <time.h>
-#undef _POSIX_C_SOURCE
-#ifdef _SAVED_POSIX_C_SOURCE
-#define _POSIX_C_SOURCE _SAVED_POSIX_C_SOURCE
-#endif
-
 #ifdef __CYGWIN__
 #include <stdlib.h>
 #include <signal.h>
@@ -80,6 +63,7 @@ OR PERFORMANCE OF THIS SOFTWARE.
 #endif
 #include <X11/Xos.h>
 #include <stdio.h>
+#include <time.h>
 #include "misc.h"
 #include <X11/X.h>
 #define XSERV_t