rewrite FormatDiagnostic to be less gross and a lot more efficient.
This also makes it illegal to have bare '%'s in diagnostics.  If you
want a % in a diagnostic, use %%.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59596 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed