Make enum process_status enumerators uppercase

Rationale: coding style consistency.
diff --git a/sysdeps/linux-gnu/events.c b/sysdeps/linux-gnu/events.c
index 52e2f4f..71d99b6 100644
--- a/sysdeps/linux-gnu/events.c
+++ b/sysdeps/linux-gnu/events.c
@@ -188,7 +188,7 @@
 		 * now) the pain of figuring this out all over again.
 		 * Petr Machata 2011-11-22.  */
 		int i = 0;
-		for (; i < 100 && process_status(pid) != ps_tracing_stop; ++i) {
+		for (; i < 100 && process_status(pid) != PS_TRACING_STOP; ++i) {
 			debug(2, "waiting for %d to stop", pid);
 			usleep(10000);
 		}