Add the break in the switch case (even if there is llvm_unreachable. It will...

Add the break in the switch case (even if there is llvm_unreachable. It will silent coverity warning CID 1231654

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@215897 91177308-0d34-0410-b5e6-96231b3b80d8