For compiling codes required for macro support, we now need swiftc
compiler in the build machine.
Unlike Darwin OSes, where swiftCore runtime is guaranteed to be present
in /usr/lib, Linux doesn't have ABI stability and the stdlib of the
build machine is not at the specific location. So the built compiler
cannot relies on the shared object in the toolchain.
This separates it from `libSwiftScan` and allows us to build this library without building much of the rest of the compiler.
Also refactor `utils/build-parser-lib` into `utils/build-tooling-libs` which builds both SwiftSyntaxParser and SwiftStaticMirror.
