[LegalizeTypes] Stop DAGTypeLegalizer::getSETCCWidenedResultTy from creating illegal...

[LegalizeTypes] Stop DAGTypeLegalizer::getSETCCWidenedResultTy from creating illegal setccs. Add checks for valid setccs

The DAGTypeLegalizer::getSETCCWidenedResultTy was widening the MaskVT, but the code in convertMask called after getSETCCWidenedResultTy had no idea this widening had occurred. So none of the operands were widened when convertMask created new setccs with the widened VT.

This patch removes the widening and adds some asserts to getNode to validate the types of setccs to prevent issues like this in the future.

Differential Revision: https://reviews.llvm.org/D53743

llvm-svn: 345428