fix building with clock_gettime and newer glibc

Building with recent glibc versions fails in gpsutils.c due to missing
definitions related to clock_gettime.  This is because we define the
_XOPEN_SOURCE macro, but not to a new enough value.  So set it to a
recent spec value that satisfies both strptime and clock_gettime.

Example build failure with glibc-2.15:
gpsutils.c: In function 'timestamp':
gpsutils.c:299:22: error: storage size of 'ts' isn't known
gpsutils.c:300:14: warning: implicit declaration of function 'clock_gettime' [-Wimplicit-function-declaration]
gpsutils.c:300:34: error: 'CLOCK_REALTIME' undeclared (first use in this function)
gpsutils.c:300:34: note: each undeclared identifier is reported only once for each function it appears in

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Eric S. Raymond <esr@thyrsus.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/gpsutils.c b/gpsutils.c
index 523838ab..3b4990a4 100644
--- a/gpsutils.c
+++ b/gpsutils.c
@@ -5,8 +5,10 @@
  */
 
 /* The strptime prototype is not provided unless explicitly requested.
- *  So add the define that POSIX says to to avoid: */
-#define _XOPEN_SOURCE
+ * We also need to set the value high enough to signal inclusion of
+ * newer features (like clock_gettime).  See the POSIX spec for more info:
+ * http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_02_01_02 */
+#define _XOPEN_SOURCE 600
 
 #include <stdio.h>
 #include <time.h>