zend: fix missing return in global register detection (GH-22206)

Author: P3p111n0

Zend/Zend.m4

@@ -317,6 +317,7 @@ int emu(const opcode_handler_t *ip, void *fp) {
   while ((*ip)());
   FP = orig_fp;
   IP = orig_ip;
+  return 0;
 }], [])],
   [php_cv_have_global_register_vars=yes],
   [php_cv_have_global_register_vars=no])