Added a new DiagnosticOptions class to swiftBasic, and added a DiagnosticOptions member to CompilerInvocation.
Added a static ParseDiagnosticArgs function to parse diagnostic-related arguments.
Added -verify to FrontendOptions.td, and added support for parsing -verify in ParseDiagnosticArgs.
Updated frontend_main() to enable and trigger the DiagnosticVerifier when -verify is passed.
Swift SVN r11318