Updates the subinvocation that builds the parseable interface to respect the
-track-system-dependencies flag of the top-level invocation if present, by
including system dependencies in the produced .swiftmodule.
In addition to being wasteful, this is a correctness issue -- the
compiler should only ever have one view of this file, and it should not
read a potentially different file after validating dependencies.
rdar://48654608
...and remove the option. This is ~technically~ CLI-breaking because
Swift 5 shipped this as a hidden driver option, but it wouldn't have
/done/ anything in Swift 5, so I think it's okay to remove.
Note that if a parseable interface (.swiftinterface) and a binary
interface (.swiftmodule) are both present, the binary one will still
be preferred. This just /allows/ parseable interfaces to be used.
rdar://problem/36885834
A ‘forwarding module’ is a YAML file that’s meant to stand in for a .swiftmodule file and provide an up-to-date description of its dependencies, always using modification times.
When a ‘prebuilt module’ is first loaded, we verify that it’s up-to-date by hashing all of its dependencies. Since this is orders of magnitude slower than reading mtimes, we’ll install a `forwarding module` containing the mtimes of the now-validated dependencies.
