[Issue 20359] core.atomic.cas throws with null as `ifThis`

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20359

--- Comment #5 from Steven Schveighoffer <schveiguy at yahoo.com> ---
OK, I see in the "allowed failure" logs. Rereading my notes for the release,
the CAS problem I fixed was related to LDC, not this bug. Sorry for the
confusion.

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