Return a StringRef in getDefaultUniversalArchName.

Patch by Stephen Drake.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213964 91177308-0d34-0410-b5e6-96231b3b80d8
Objective-C. Warn if protocol used in an @protocol
expression is a forward declaration as this results
in undefined behavior. rdar://17768630


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213968 91177308-0d34-0410-b5e6-96231b3b80d8