Fix PHP 8.0 tests under ZTS

Author: johnpbloch

php_zookeeper.h

@@ -42,7 +42,10 @@ extern zend_module_entry zookeeper_module_entry;
 #define TSRMLS_CC
 #define TSRMLS_FETCH()
 #define TSRMLS_FETCH_FROM_CTX(z)
-#define tsrm_set_interpreter_context(z)
+void *tsrm_set_interpreter_context(void *new_ctx)
+{
+	return NULL;
+}
 #endif // if PHP >= 8.0
 #endif