fix upg: disable c99 warn about flexible array

Disable warning introduced in 2fad38a

---

Pull Request resolved: #1166

Co-authored-by: kpavlov00 <kpavlov00@yandex-team.com>
commit_hash:462134674cf55abff30daf615d55edc92f0da1ba

Author: 2 people

postgresql/src/storages/postgres/detail/cancel.cpp

@@ -22,6 +22,11 @@ typedef struct {
 
 #if USERVER_LIBPQ_VERSION >= 180000
 
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc99-extensions"
+#endif
+
 struct pg_cancel {
     SockAddr raddr;          /* Remote address */
     int be_pid;              /* PID of to-be-canceled backend */
@@ -38,6 +43,10 @@ struct pg_cancel {
     char cancel_req[/*FLEXIBLE_ARRAY_MEMBER*/]; /* CancelRequestPacket */
 };
 
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
 #else
 
 // NOLINTNEXTLINE(cppcoreguidelines-macro-usage)