DMD emits hardcoded calls to core.atomic

[TurkeyMan]

DMD seems to hard-wire calls to core.atomic functions; it'd be great to audit and remove all these hard-wired module references, use either extern(C) or __d_cas, __d_atomicLoad, etc expected in object.d (which shim to core.atomic in druntime)?

[ibuclaw]

@Geod24