Hexagon TC: Move getHexagonTargetCPU from Tools.cpp to
 ToolChains.cpp

This is in anticipation of forthcoming library path changes.

Also ...
- Fixes some inconsistencies in how the arch is passed to tools.
- Add test cases for various forms of arch flags

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169505 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed