GNU C library for struct tm has 2 additional fields.

Summary:
initialize 2 additional fields tm_gmtoff and tm_zone,
otherwise under strict warnings for initialization, we get errors
in myrocks.
Closes https://github.com/facebook/rocksdb/pull/2439

Differential Revision: D5229013

Pulled By: yiwu-arbug

fbshipit-source-id: 9fc1615a1919656f36064791706ed41e10e9db84

env/mock_env.cc

@@ -378,7 +378,8 @@ class TestMemLogger : public Logger {
       struct timeval now_tv;
       gettimeofday(&now_tv, nullptr);
       const time_t seconds = now_tv.tv_sec;
-      struct tm t{0, 0, 0, 0, 0, 0, 0, 0, 0};
+      struct tm t;
+      memset(&t, 0, sizeof(t));
       auto ret __attribute__((__unused__)) = localtime_r(&seconds, &t);
       assert(ret);
       p += snprintf(p, limit - p,