Submitted by: Bill Wendling

Reviewed by: Chris Lattner

- Created a base class (TextDiagnostics) for all text diagnostic classes.
  Moved the "IgnoreDiagnostic" method up there, and created a method that
  will format the diagnostic string, replacing %# with the appropriate
  string. This is in preparation for adding a text diagnostic checker.

llvm-svn: 39650