Towards PR12457: constant expression evaluation support for...

Towards PR12457: constant expression evaluation support for __builtin_parity{,l,ll}, __builtin_ffs{,l,ll}, and __builtin_fpclassify.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183889 91177308-0d34-0410-b5e6-96231b3b80d8