Clang no longer supports `-working-directory<path>`. Split this argument
into `-working-directory <path>` so that clients passing the old
argument still work.
Pass a wrapped VFS down into `clang::createInvocationFromCommandLine` so
that the working directory is set and then used in the underlying Clang
`CompilerInstance`.
Fixes the possibility of differing modules hashes when the same
arguments are used in Clang directly vs from the importer.
Resolves rdar://79376364
