This is important for performance diagnostics: it’s assumed that (non-generic) MemoryLayout constants do not need to create metadata at runtime. At Onone this is only guaranteed if the TargetConstantFolding pass runs.
rdar://94836837
lit.py currently allows any substring of `target_triple` to be used as a
feature in REQUIRES/UNSUPPORTED/XFAIL. This results in various forms of
the OS spread across the tests and is also somewhat confusing since they
aren't actually listed in the available features.
Modify all OS-related features to use the `OS=` version that Swift adds
instead. We can later remove `config.target_triple` so that these don't
the non-OS versions don't work in the first place.
