[InstCombine] We folded an fcmp to an i1 instead of a vector of i1

Remove an ad-hoc transform in InstCombine and replace it with more
general machinery (ValueTracking, InstructionSimplify and VectorUtils).

This fixes PR27332.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266175 91177308-0d34-0410-b5e6-96231b3b80d8