For ID counters and standalone flags (most sites), drop to .relaxed
since nothing reads other memory based on the atomic's value.
MultiEntrySemaphore.signaled is the exception: it is used as a
signal/wait primitive where waiters proceed to use state set up
before signal(). Use .releasing on store and .acquiring on load so
that pre-signal writes are visible to waiters that observe `true`.
.relaxed there would be incorrect on weakly-ordered architectures.
Rintaro Ishizaki
a6c926fa34