In LLVM unified builds `%swift_obj_root` points to `<LLVM build dir>/tools/swift`,
and folders like `bin`, `lib` and `share` are not under `swift_obj_root`, which
makes some tests fail.
For the cases in which `%swift_obj_root/lib` was used, replace it by
using `%swift-lib-dir` instead. Replicate `%swift-lib-dir` to create
`%swift-bin-dir` and `%swift-share-dir`, and use those instead of
`%swift_obj_root/bin` and `%swift_obj_root/share`.
This alternates work both in Swift build-script builds and also in LLVM
unified builds.
This will mean that '-disable-implicit-swift-modules' also automatically implies two things:
1. Clang modules must also be explicit, and the importer's clang instance will get '-fno-implicit-modules' and '-fno-implicit-module-maps'
2. The importer's clang instance will no longer get a '-fmodules-cache-path=', since it is not needed in explicit builds
In case the compiler is used with concurrency features enabled (by-default or otherwise), and an older SDK is used which does not include the `_Concurrency` module, do not load this module implicitly. Instead, emit a diagnostic indicating that no such module is found.
rdar://76967260
