Remove Diagnostic.h include from Preprocessor.h.

- Move the offending methods out of line and fix transitive includers.
- This required changing an enum in the PPCallback API into an unsigned.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149782 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed