RegionInfo: Use report_fatal_error instead of llvm_unreachable

Otherwise when using -verify-region-info in a release build the
error won't be emitted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321878 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed