Add -Wno-implicit-fallthrough compiler flag for OpCache

Author: Girgias

ext/opcache/config.m4

@@ -313,7 +313,7 @@ int main() {
 	shared_alloc_mmap.c \
 	shared_alloc_posix.c \
 	$ZEND_JIT_SRC,
-	shared,,-DZEND_ENABLE_STATIC_TSRMLS_CACHE=1,,yes)
+	shared,,"-Wno-implicit-fallthrough -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1",,yes)
 
   PHP_ADD_EXTENSION_DEP(opcache, pcre)