Optional (unsafe) cfg to use atomic builtins on targets where atomic CAS is not supported, or on atomic operations of unsupported sizes #33
Description
Split from #26.
Use atomic builtins. (Let the user implement the actual atomic logic.) (multi-core safety: implementation-dependent)
See this comment for problems I am aware of.
implementation: Add cfg to use__atomic_*builtins #30
Should be unsafe cfg.