Remove this distinction without a difference. Originally, the thought
was to
1) Isolate the cross-module build infrastructure
2) Provide a signal to the driver that a dependency had swiftdeps info
in it
But the driver need only notice swiftmodule files as external
dependencies and try to extract that information if it can to divine the
signal it needs. Additionally, we can give it fingerprints as priors to
let it know there might be incremental info to be had.
Switch from a string core to a 128-bit integral core. This should make
Fingerprints much cheaper to copy around and sets us up for a future
where we can provide alternative implementations of the ambient hashing
algorithm.
rdar://72313506
