[VirtRegMap] Fix for PR17825. Do not ignore noreturn definitions when setting
isPhysRegUsed if the unwind information is required.
Indeed, the runtime may need a correct stack to be able to unwind the call.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194271 91177308-0d34-0410-b5e6-96231b3b80d8