Only use SA_RESTART if it exists

Fixes build on QNX (and possibly HPUX given Bug 168352)
Patch essentially from pkgsrc devel/glib2/patches/patch-ai

https://bugzilla.gnome.org/show_bug.cgi?id=583321

glib/gmain.c

@@ -4963,7 +4963,11 @@ ref_unix_signal_handler_unlocked (int signum)
       struct sigaction action;
       action.sa_handler = g_unix_signal_handler;
       sigemptyset (&action.sa_mask);
+#ifdef SA_RESTART
       action.sa_flags = SA_RESTART | SA_NOCLDSTOP;
+#else
+      action.sa_flags = SA_NOCLDSTOP;
+#endif
       sigaction (signum, &action, NULL);
     }
 }