Rename DiagnosticInfoOptimizationWarning to DiagnosticInfoOptimizationFailure
so the severity of the message is not part of the type name.

Reviewed by Alp Toker


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213399 91177308-0d34-0410-b5e6-96231b3b80d8