CPP: Add suport for thread-safety on Linux and Mac in non-Boost base/.

This is needed for Chrome on Android which is the only Chrome port that
requires thread-safety.

R=lararennie@google.com

Review URL: https://codereview.appspot.com/10244046

git-svn-id: http://libphonenumber.googlecode.com/svn/trunk/cpp/src/phonenumbers@583 ee073f10-1060-11df-b6a4-87a95322a99c
5 files changed