Fix build with clang

PUBLISHED_FROM=0cec0e6db4f46a76130fa7b6ec955d4151b28aae

mongoose.c

@@ -511,6 +511,9 @@ int mkdir(const char *path, mode_t mode) {
 #endif /* CS_ENABLE_SPIFFS */
 
 #endif /* EXCLUDE_COMMON */
+
+/* ISO C requires a translation unit to contain at least one declaration */
+typedef int cs_dirent_dummy;
 #ifdef MG_MODULE_LINES
 #line 0 "./src/../../common/cs_time.c"
 #endif