0072c95aff
enable Atomic*.{load,store} for ARMv6-M / MSP430 closes #45085 as proposed in https://github.com/rust-lang/rust/issues/45085#issuecomment-384825434 this commit adds an `atomic_cas` target option and extends the `#[cfg(target_has_atomic)]` attribute to enable a subset of the `Atomic*` API on architectures that don't support atomic CAS natively, like MSP430 and ARMv6-M. r? @alexcrichton