Using `SwiftSDK.deriveTargetSwiftSDK`, which is the same method that SwiftPM's own CLI tools use to determine the SDK from passed-in info (target `--triple`, `--swift-sdk`, and host sdk). This allows us to better uphold the contract in the [Configuration File](d11c101ce2/Documentation/Configuration%20File.md (structure)) docs, namely that the `swiftSDK` param is "Equivalent to SwiftPM's `--swift-sdk` option" and similarly for `triple`.
As concrete examples of where (AFAICT) the current implementation diverges:
- Passing a `--triple` of `wasm32-unknown-wasi` to `swift-build` will use the toolchain-integrated Wasm SDK if one exists. Passing the same value to sourcekit-lsp does not do this.
- Perhaps more relevant: after landing https://github.com/swiftlang/swift-package-manager/pull/6828, this change will make it so that building for iOS is as simple as setting `"triple": "arm64-apple-ios"` in the config! Currently, it's necessary to set C/Swift flags and hardcode the sysroot. Should close https://github.com/swiftlang/sourcekit-lsp/issues/1587.
This PR depends on:
- https://github.com/swiftlang/swift-package-manager/pull/7925
Do one of the following for every `FIXME` or `TODO` comment
- Add an issue that tracks the task
- Remove the comment if we are not planning to address it
The SwiftPM build system integration was the only one in its own modules. Merge it into the `BuildSystemIntegration` modules next to eg. the compilation database build system.
