[Issue 11188] std.math.abs fails for shared BigInt type

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=11188

--- Comment #13 from anonymous4 <dfj1esp02 at sneakemail.com> ---
Indeed, but it's still big and shallow mutable. How would you avoid tearing? It
suggests different data layout with increased pressure on GC.

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