configure: Globally define AC_GNU_SOURCE

We were using _GNU_SOURCE throughout the codebase, so simply define it
once during configure. This is the easiest method to enable recursive
mutexes using pthreads, as required in a pending patch.

boilerplate/cairo-boilerplate-pdf.c

@@ -30,6 +30,10 @@
 #include <cairo-pdf-surface-private.h>
 #include <cairo-paginated-surface-private.h>
 
+#if HAVE_SIGNAL_H
+#include <signal.h>
+#endif
+
 #if ! CAIRO_HAS_RECORDING_SURFACE
 #define CAIRO_SURFACE_TYPE_RECORDING CAIRO_INTERNAL_SURFACE_TYPE_RECORDING
 #endif

boilerplate/cairo-boilerplate-ps.c

@@ -31,6 +31,10 @@
 #include <cairo-ps-surface-private.h>
 #include <cairo-paginated-surface-private.h>
 
+#if HAVE_SIGNAL_H
+#include <signal.h>
+#endif
+
 #if ! CAIRO_HAS_RECORDING_SURFACE
 #define CAIRO_SURFACE_TYPE_RECORDING CAIRO_INTERNAL_SURFACE_TYPE_RECORDING
 #endif

configure.ac

@@ -3,6 +3,7 @@ CAIRO_PARSE_VERSION
 AC_INIT([cairo],
 	[cairo_version_major.cairo_version_minor.cairo_version_micro],
 	[http://bugs.freedesktop.org/enter_bug.cgi?product=cairo])
+AC_USE_SYSTEM_EXTENSIONS
 AC_CONFIG_SRCDIR(src/cairo.h)
 AC_CONFIG_HEADERS(config.h)
 AC_CONFIG_AUX_DIR(build)
@@ -13,6 +14,8 @@ AC_PROG_LIBTOOL dnl ([1.4]) Don't remove!
 DOLT dnl Make my libtool fast!
 GTK_DOC_CHECK([1.6])
 
+AC_GNU_SOURCE
+
 dnl ===========================================================================
 dnl
 dnl The order of the includes here is rather important

src/cairo-gstate.c

@@ -35,8 +35,6 @@
  *	Carl D. Worth <cworth@cworth.org>
  */
 
-#define _GNU_SOURCE
-
 #include "cairoint.h"
 
 #include "cairo-clip-private.h"

src/cairo-matrix.c

@@ -34,8 +34,6 @@
  *	Carl D. Worth <cworth@cworth.org>
  */
 
-#define _GNU_SOURCE
-
 #include "cairoint.h"
 #include "cairo-error-private.h"
 

src/cairo-scaled-font.c

@@ -38,8 +38,6 @@
  *      Chris Wilson <chris@chris-wilson.co.uk>
  */
 
-#define _GNU_SOURCE
-
 #include "cairoint.h"
 #include "cairo-error-private.h"
 #include "cairo-scaled-font-private.h"