[test] Fix xrsimulator lit failures via mock SDK VersionMap (#90672) (#90963)
A few xrsimulator tests currently fail to infer the correct visionOS
version and falsely see SwiftStdlib 5.x symbols as unavailable.
This PR fixes those tests by:
- Adding `SDKSettings.json` to the shared
`test/Inputs/clang-importer-sdk` to provide a correct version map
- Pinning the CC target triple in `IDE/print_clang_header_i386.swift` as
a result of the first change. Once the mock SDK carries an
`SDKSettings.json`, clang's Darwin driver derives the target from the
SDK as `i386-apple-<CanonicalName>`, which is not a valid target with a
working Swift stdlib. Pinning `%target-triple` preserves the historical
behavior.
(cherry picked from commit e3f3a9335a70d1f9f7604299db511712777326d4)
Signed-off-by: Duo Wang <duo_wang@apple.com>