Make google-build-using-namespace skip std::.*literals

Summary:
C++14 added a couple of user-defined literals in the standard library. E.g.
std::chrono_literals and std::literals::chrono_literals . Using them
requires a using directive so do not warn in google-build-using-namespace
if namespace name starts with "std::" and ends with "literals".

Reviewers: alexfh

Reviewed By: alexfh

Subscribers: cfe-commits

Patch by Martin Ejdestig!

Differential Revision: https://reviews.llvm.org/D33010

llvm-svn: 303085