Don't try to figure out the executable names during replay from
libSwiftScan.dylib. The actual executable path for the process actually
doesn't matter in this case to reconstruct the invocation and might
actually be misleading.
Just use `swift-frontend` as a placeheader executable name for
in-process cache replay.
rdar://132758308
Add support for serialized diagnostics, parseable output, and other
kinds of output from diagnostics engine to the libSwiftScan
replayCompilation API.
rdar://129015959
