Give CGDebugInfo::getContextDescriptor a more specific return type

Not that the DI* hierarchy is terribly type safe, but this makes the contract a
little clearer I think.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179835 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed