Add compatibility for non GNU strerror_r.

Needed for libraries like musl that do not implement the GNU variant.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

traceevent/event-parse.c

@@ -5121,12 +5121,17 @@ int pevent_strerror(struct pevent *pevent __maybe_unused,
 	const char *msg;
 
 	if (errnum >= 0) {
+#if defined(__GLIBC__)
 		msg = strerror_r(errnum, buf, buflen);
 		if (msg != buf) {
 			size_t len = strlen(msg);
 			memcpy(buf, msg, min(buflen - 1, len));
 			*(buf + min(buflen - 1, len)) = '\0';
 		}
+#else
+		if (strerror_r(errnum, buf, buflen))
+			snprintf(buf, buflen, "errnum %i", errnum);
+#endif
 		return 0;
 	}