[patch] simplifyCFG for review

[Ye, Mei]

Hi all

Thank you for your comments.   Attached is an updated patch.
- add TargetTransformInfo to R600 .
- add hasBranchDivergence to query whether a target has branch divergence.
- Invoke branch reduction opts only when the underlying target has branch divergence.  So currently it only gets triggered for R600.
- fixed a bug in opt.cpp
- correct clang-format issues.

I have tested the correctness on x86 (by adding branch divergence to X86TargetTransformInfo in my local workspace) using existing testing infrastructure and CPU2006, CPU2000.  Tom Stellard agrees to run R600 testings (thanks a lot, Tom).

-Mei
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