This change introduces a new compilation target platform to the Swift compiler - visionOS.
- Changes to the compiler build infrastrucuture to support building compiler-adjacent artifacts and test suites for the new target.
- Addition of the new platform kind definition.
- Support for the new platform in language constructs such as compile-time availability annotations or runtime OS version queries.
- Utilities to read out Darwin platform SDK info containing platform mapping data.
- Utilities to support re-mapping availability annotations from iOS to visionOS (e.g. 'updateIntroducedPlatformForFallback', 'updateDeprecatedPlatformForFallback', 'updateObsoletedPlatformForFallback').
- Additional tests exercising platform-specific availability handling and availability re-mapping fallback code-path.
- Changes to existing test suite to accomodate the new platform.
The "#if compiler(>=5.3) && $AsyncAwait" checks were necessary for
staging in concurrency in Swift 5.5. At this point, it's safe to assume
that any compiler that tries to read a generated Swift interface file will
support concurrency, so we can stop emitting these guards.
Some decls that are expected to be synthesized for distributed actors are
printed explicitly in swiftinterfaces so diagnostics and assertions need to
take that possibility into account.
Resolves rdar://108533918
