Make runtime code warning-free with -std=c89

The endif-labels warning warns on this code excerpt, so remove the
tokens after the endif directive.

Author: Jugst3r

tools/gnatcov/rts/gnatcov_rts_c-memory.h

@@ -41,4 +41,4 @@ extern "C"
 #ifdef __cplusplus
 }
 #endif
-#endif // GNATCOV_RTS_C_MEMORY_H
+#endif