Fix #1481 - use stricter compilation flags

test/mongoose_custom.c

@@ -33,5 +33,6 @@ struct mg_connection *mg_mkpipe(struct mg_mgr *mgr, mg_event_handler_t fn,
   return NULL;
 }
 
+void _fini(void);
 void _fini(void) {
 }

test/pack.c

@@ -25,6 +25,8 @@
 #include <sys/stat.h>
 
 static const char *code =
+    "const char *mg_unpack(const char *path, size_t *size, time_t *mtime);\n"
+    "const char *mg_unlist(size_t no);\n"
     "const char *mg_unlist(size_t no) {\n"
     "  return packed_files[no].name;\n"
     "}\n"