FrontendTool sets up diagnostic infrastructure early and suppresses stdout diagnostics if frontend-parseable-output is enabled. It then calls `CompilerInstance.setup` which may fail - if it fails, we exit early. But that means we have not gotten a chance to emit parseable-output.
This change moves emission of the `began` parseable message to before `CompilerInstance.setup`, and ensures that a corresponding `finished` message is emitted if the setup fails.
Resolves rdar://93187783
