[Issue 18140] experimental allocators, bitmapped_block UB on OSX 64 bits

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18140

Basile B. <b2.temp at gmx.com> changed:

           What    |Removed                     |Added
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           Severity|normal                      |blocker

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