Add getSelect helper function

Patch by Micah Villmow from last year that was reviewed, but never committed

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184011 91177308-0d34-0410-b5e6-96231b3b80d8
Introduce getSelect usage and use more getSelectCC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184012 91177308-0d34-0410-b5e6-96231b3b80d8