A StringRef-ication of the DiagnosticIDs API and internals.

Patch by Matthieu Monrocq with tweaks by me to avoid StringRefs in the static
diagnostic data structures, which resulted in a huge global-var-init function.

Depends on llvm commit r132046.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@132047 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed