swift234

[SR-1639][SourceKit] Link SwiftLang libraries to sourcekitd

When building SourceKit on Linux, sourcekitdAPI would not be linked to
SourceKitSwiftLang, which caused the following symbols to be undefined:

- `SourceKit::LangSupport::SynthesizedUSRSeparator`
- `SourceKit::LangSupport::createSwiftLangSupport(SourceKit::Context&)`

Link SourceKitSwiftLang to resolve these symbols.