Bring back r250262: PS4 toolchain

There was a minor problem with a test. Sorry for the noise yesterday.

This patch adds missing pieces to clang, including the PS4 toolchain
definition, added warnings, PS4 defaults, and Driver changes needed for
our compiler.

A patch by Filipe Cabecinhas, Pierre Gousseau and Katya Romanova!

Differential Revision: http://reviews.llvm.org/D13482

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@250293 91177308-0d34-0410-b5e6-96231b3b80d8