Limit GCC 6 pragmas.

-Wnull-dereference and -Wshift-overflow are new warnings in GCC 6, so do
not try to disable them with pragmas on older GCC versions.

Fixes commit a8e15ea924.

builder/yajl-c.c

@@ -31,7 +31,9 @@
 /* GCC can't work out that the YAJL_IS_<foo> test is sufficient to
  * ensure that YAJL_GET_<foo> later doesn't return NULL.
  */
+#if defined(__GNUC__) && __GNUC__ >= 6 /* gcc >= 6 */
 #pragma GCC diagnostic ignored "-Wnull-dereference"
+#endif
 
 #define Val_none (Val_int (0))
 

daemon/debug.c

@@ -990,7 +990,9 @@ do_internal_rhbz914931 (int count)
 }
 
 #pragma GCC diagnostic push
+#if defined(__GNUC__) && GUESTFS_GCC_VERSION >= 60000 /* gcc >= 6 */
 #pragma GCC diagnostic ignored "-Wnull-dereference"
+#endif
 
 static void
 deliberately_cause_a_segfault (void)

daemon/ldm.c

@@ -35,7 +35,9 @@
 /* GCC can't work out that the YAJL_IS_<foo> test is sufficient to
  * ensure that YAJL_GET_<foo> later doesn't return NULL.
  */
+#if defined(__GNUC__) && GUESTFS_GCC_VERSION >= 60000 /* gcc >= 6 */
 #pragma GCC diagnostic ignored "-Wnull-dereference"
+#endif
 
 GUESTFSD_EXT_CMD(str_ldmtool, ldmtool);
 

p2v/gui.c

@@ -69,7 +69,9 @@
 /* errors in <gtk.h> */
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wstrict-prototypes"
+#if defined(__GNUC__) && __GNUC__ >= 6 /* gcc >= 6 */
 #pragma GCC diagnostic ignored "-Wshift-overflow"
+#endif
 #include <gtk/gtk.h>
 #pragma GCC diagnostic pop
 

p2v/main.c

@@ -36,7 +36,9 @@
 /* errors in <gtk.h> */
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wstrict-prototypes"
+#if defined(__GNUC__) && __GNUC__ >= 6 /* gcc >= 6 */
 #pragma GCC diagnostic ignored "-Wshift-overflow"
+#endif
 #include <gtk/gtk.h>
 #pragma GCC diagnostic pop