Cannot compile on macOS Catalina due to depreciated atomics

[bearbearfoxsquirrel]

Hi,
Just wanted to give notification of a compilation issue on macOS Catalina.

Upon trying to compile you are greeted with the following error:

'OSAtomicCompareAndSwap64Barrier' is deprecated: first deprecated in macOS 10.12 - Use std::atomic_compare_exchange_strong() from <atomic> instead

This is a trivially fixed issue, but it took a little time to fix on my machine; finding all the usages and replacing them.

Best wishes,
Michael :)