Throw the switch to allow FastISel to emit instructions whose return types different...

Throw the switch to allow FastISel to emit instructions whose return types different from their inputs.  Next step: adding lowering pattens in FastISel that actually use these newly available opcodes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55349 91177308-0d34-0410-b5e6-96231b3b80d8