This is a headache for users:

As the message explains, VS 2015 RTW and VS 2015 Update 1 emitted an incorrect layout for this scenario, std::atomic<T> with sizeof(T) equal to 2/4/8 and alignof(T) < sizeof(T). Everything compiled with VS 2015 Update 2, VS 2015 Update 3 (the final update), VS 2017, and VS 2019 is immune to this problem.

Now that it's been almost 5 years, does it still make sense to require users to define this macro in order to compile Standard-conformant code? Do we have to worry about separately compiled OBJs/LIBs built with VS 2015 RTW/Update 1 still lurking out there? (Hopefully, this macro should have brought such code to someone's attention.)

I believe it's time to remove this check, but we need to make a decision.