cpp: Fix an OpenBSD compilation error that appears to be a real bug

The (Linux) man page for ctime_r states pretty clearly that
the buffer it uses must have space for at least 26 characters.

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@776925 13f79535-47bb-0310-9956-ffa450edef68
1 file changed