Uniformly define _XOPEN_SOURCE to 600.

The feature_tests.h header from Sun systems (Solaris/OpenSolaris) will abort
the build if _XOPEN_SOURCE is defined to 500, and C99 is requested (as well
as POSIX.1-2001), and will only accept it to be defined to 600.
inspired by a patch from Diego Pettenò, flameeyes gmail com

Originally committed as revision 15460 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -20,7 +20,7 @@
  */
 
 /* needed for usleep() */
-#define _XOPEN_SOURCE 500
+#define _XOPEN_SOURCE 600
 
 #include "config.h"
 #include <ctype.h>

libavcodec/utils.c

@@ -26,7 +26,7 @@
  */
 
 /* needed for mkstemp() */
-#define _XOPEN_SOURCE 500
+#define _XOPEN_SOURCE 600
 
 #include "libavutil/integer.h"
 #include "libavutil/crc.h"

libavformat/rtpdec.c

@@ -20,7 +20,7 @@
  */
 
 /* needed for gethostname() */
-#define _XOPEN_SOURCE 500
+#define _XOPEN_SOURCE 600
 
 #include "libavcodec/bitstream.h"
 #include "avformat.h"