[x32] Adding X32 target support to driver, including TargetInfo,DescriptionString, flags, paths lookup, etc. Cover changes with new tests. The author of the patch is Pavel Chupin (@pavel.v.chupin).
The changes enable "hello world" on x32 target (x86_64-*-linux-gnux32). s/isX32/IsX32/ also fixed.

Differential Revision: http://reviews.llvm.org/D4180