Using a virutal output backend to capture all the outputs from
swift-frontend invocation. This allows redirecting and/or mirroring
compiler outputs to multiple location using different OutputBackend.
As an example usage for the virtual outputs, teach swift compiler to
check its output determinism by running the compiler invocation
twice and compare the hash of all its outputs.
Virtual output will be used to enable caching in the future.
Use the std-equivalent names as the LLVM ones are now deprecated
(eventually `llvm::Optional` will disappear):
- `getValue` -> `value`
- `getValueOr` -> `value_or`
- `hasValue` -> `has_value`
Follow up from ab1b343dad and
7d8bf37e5e with some missing cases.
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
