Merge pull request #21416 from stanley-cheung/php-fix-5_5-build

PHP: fix php5.5 build

src/php/ext/grpc/php_grpc.c

@@ -26,6 +26,7 @@
 #include "call_credentials.h"
 #include "server_credentials.h"
 #include "completion_queue.h"
+#include <inttypes.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>