Eliminate the atomic porability header's dependence on Windows.h
Eliminate the atomic porability header's dependence on Windows.h

Summary:
This is done by using the intrinsic directly instead.
This also marks the input parameter as `volatile`, to make it more clear that that's how it is handled by `_InterlockedExchangeAdd64`.

Reviewed By: yfeldblum

Differential Revision: D3671320

fbshipit-source-id: 6010085ec3b6952a3eb1e952965ec6ad87566db2

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