[SimplifyCFG] NFC, update Switch tests to better examine successive patches

[SimplifyCFG] NFC, update Switch tests to better examine successive patches

Also add baseline tests to show effect of later patches.

There were a couple of regressions here that were never caught,
but my patch set that this is a preparation to will fix them.

Differential Revision: https://reviews.llvm.org/D61150

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363226 91177308-0d34-0410-b5e6-96231b3b80d8