This change adds a frontend flag, -verify-additional-file, which can be used to pass extra files directly to the diagnostic verifier. These files are not otherwise considered to be Swift source files; they are not compiled or even properly parsed.
This feature can be used to verify diagnostics emitted in non-source files, such as in module interfaces or header files.
Request-based incremental dependencies are enabled by default. For the time being, add a flag that will turn them off and switch back to manual dependency tracking.
When enabled at the driver level, the frontends will inherit the flag. For each frontend that recieves this option, all primaries will have their reference dependencies validated.
Enables Chris's auto-apply-fixes mode for -verify: if an expected-*
annotation has the wrong message, or if the expected fix-its are
incorrect, this option will **edit the original file** to update them.
This is a tool for compiler developers only; it doesn't affect
normal diagnostic printing or normal fix-its.
