Add needed functions to glibc-compat for pkg

ports/glibc-compat/src/timegm.c

+/* Copyright 2015 The Native Client Authors. All rights reserved.

[Sam Clegg, 2015/07/28 00:14:13]

nit: put /* and */ on lines be themselves to match other files in this
directory.

[zhitingzhu, 2015/07/28 02:05:41]

Done.

+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file. */
+// pull from freebsd 10.1 ./contrib/ldns/compat/timegm.c
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+time_t
+timegm (struct tm *tm) {
+  time_t ret;
+  char *tz;
+
+  tz = getenv("TZ");
+  putenv((char*)"TZ=");
+  tzset();
+  ret = mktime(tm);
+  if (tz) {
+    char buf[256];
+    snprintf(buf, sizeof(buf), "TZ=%s", tz);
+    putenv(tz);
+  }
+  else
+    putenv((char*)"TZ");
+  tzset();
+  return ret;
+}