GB-130 33.5.2 [atomics.syn] memory_order_acquire etc should be freestanding

[wg21bot]

The std::memory_order variables were moved to the <atomic> synopsis after P1642R11 added"freestanding" to everything in that synopsis, so didn't get marked as freestanding. They should be available for freestanding.

It's not entirely clear whether the enumerators for the std::memory_order enum type are also freestanding, as those enumerators aren't shown in the synopsis, only in [atomics.order]

Ensure that the enumerators of memory_order and the variables of that type are freestanding.

[JeffGarland]

This is partially addressed by LWG 3753 and the rest by LWG 3814

[jensmaurer]

Accepted.