Tests: un-skip a few libc++ tests that were believed to have timing assumptions

[cpplearner]

• std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp
  • The timing assumption has been removed by llvm/llvm-project@b3b611f and llvm/llvm-project@e98195f.
• std/thread/thread.mutex/thread.lock/thread.lock.guard/adopt_lock.pass.cpp
  • The timing assumption has been removed by llvm/llvm-project@a675c1d.
• std/thread/thread.mutex/thread.lock/thread.lock.guard/mutex.pass.cpp
  • The timing assumption has been removed by llvm/llvm-project@a675c1d.
• std/thread/thread.threads/thread.thread.class/thread.thread.destr/dtor.pass.cpp
  • It doesn't seem to have timing assumptions. (There's a sleep_for call, which seems redundant.)
• std/thread/thread.threads/thread.thread.class/thread.thread.member/detach.pass.cpp
  • It doesn't seem to have timing assumptions.

Drive-by: move two XFAIL: msvc tests down to "XFAILs WHICH PASS" section.

[StephanTLavavej]

I'm nervous about anything that says "detach", but if it flakes out we can re-skip it. Thanks!

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for improving our libc++ test coverage! ✅ 🎉 😸