Compiler output at least up to serialization should be deterministic at this point,
at least when not taking SIL into account. This /should/ mean that changing a
function body should not affect the final built swiftmodule, which means downstream
targets don't need to be rebuilt. Leaving the previous swiftmodule output in place
signals that.
A while back I put in a push to get all the non-determinism out of type checking,
importing, and serialization itself; it looks like we've finally made it. Let's keep
it that way!
rdar://problem/20539158 and others
Swift SVN r29923
