Zend/zend_system_id.h: add missing include

For BEGIN_EXTERN_C, ZEND_API.

Author: MaxKellermann

Zend/zend_system_id.h

@@ -17,6 +17,8 @@
 #ifndef ZEND_SYSTEM_ID_H
 #define ZEND_SYSTEM_ID_H
 
+#include "zend_API.h"
+
 BEGIN_EXTERN_C()
 /* True global; Write-only during MINIT/startup */
 extern ZEND_API char zend_system_id[32];