[6.2] Allow linking _Concurrency for WASI with Embedded Swift (#1865)

Cherry-pick of #1863.

**Explanation**: Currently, when building packages for WASI with Embedded Swift, libraries such as `libswift_Concurrency.a` and `libswift_ConcurrencyDefaultExecutor.a` are not discoverable and require passing `-Xlinker <swift-sdk-path>/usr/lib/swift/embedded/wasm32-unknown-wasip1` option manually. This path can be inferred by the driver, which simplifies build invocations for users significantly, while the rest of linkage options (`-lswift_Concurrency` etc) can be specified in toolset files.
**Scope**: Limited to Embedded Swift for Wasm.
**Risk**: Low due to limited scope.
**Testing**: Added new automated test cases.
**Issue**: rdar://148820885
**Reviewer**: @kateinoigakukun

Author: MaxDesiatov