[PATCH] Add DiagnosticSuppressionScope RAII class

[Brad King]

On 11/19/2014 11:22 PM, Richard Smith wrote:
> once you enter this mode, you can't
> reasonably leave it again. For that, you can just set the
> SuppressAllDiagnostics flag on the DiagnosticsEngine.

SuppressAllDiagnostics prevents DiagnosticErrorTrap from working
so any analysis in Clang that uses traps fails to work correctly.
We need error traps to work for correct analysis but no actual
diagnostics to be emitted or output files aborted.

-Brad