GenMC should work fine on macOS, but there are multiple things that need to be done before we can enable it in Miri:

• (non-blocking) there's some odd warning about filename cases (also see Zulip).
• The test suite seems to get stuck on CI, I don't know which test it is stuck in (see this CI log). This part will probably require actual macOS hardware to further analyze, which I do not have.
• When I run the test suite for an apple target locally, the std tests fail. This is somewhat expected because we didn't wire up the mutex shims on macOS, but what's surprising is that we get an "access to uninit memory" error. I think that's an instance of this. We should probably redirect the pthread APIs to genmc when running in genmc mode.