Add constant evaluation support for __builtin_isinf, __builtin_isfinite,
__builtin_isnan, and __builtin_isnormal. Patch by Karthik Bhat! Tests by me.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192729 91177308-0d34-0410-b5e6-96231b3b80d8