[guix] Consistently use FHS for all targets

Summary: This requires a bump in the time machine commit to a bugfix commit for OSX, and to bump the clang version (version 15 is used).

Test Plan: Run the GUIX builds.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17216