driver: Fix -working-dir for foreign files

-working-dir definitely needs more serious testing, there are some easy ways to test this.

• Modify Cabal to call ghc using -working-dir rather than changing directory.
• Modify the testsuite to run ghc using -working-dir rather than running GHC with cwd = temporary directory.

However this will have to wait until after 9.12.

Fixes #25150 (closed)