Support non-atomic targets #1089
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As of rust-lang/rust#51953 `cfg(target_has_atomic)` has been updated to separately enable compare-and-swap (CAS) operations from the different supported sizes. Because `AtomicWaker` uses these CAS operations we need to also gate its inclusion on `cfg(target_has_atomic = "cas")`. `thumv6m` is one of the architectures that supports atomic read-write operations on its pointer sized integers, but doesn't support CAS operations.
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As of rust-lang/rust#51953
cfg(target_has_atomic)has been updated to separately enable compare-and-swap (CAS) operations from the different supported sizes. BecauseAtomicWakeruses these CAS operations we need to also gate its inclusion oncfg(target_has_atomic = "cas").thumv6mis one of the architectures that supports atomic read-write operations on its pointer sized integers, but doesn't support CAS operations.