This has the effect of switching the vendor and OS from "none-unknown" to "unknown-none" in the normalized triple, to better reflect that the bare metal target has no OS, rather than an unknown one.
The cmake script and multilib templates have various hardcoded references to triples which now need changing.
The way in which clang normalizes certain target triples was recently changed:
https://github.com/llvm/llvm-project/pull/89638
This has the effect of switching the vendor and OS from "none-unknown" to "unknown-none" in the normalized triple, to better reflect that the bare metal target has no OS, rather than an unknown one.
The cmake script and multilib templates have various hardcoded references to triples which now need changing.