[Issue 23445] Can leak scope variable through delegate context

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23445

--- Comment #6 from timon.gehr at gmx.ch ---
The delegate context is allocated on the heap. There is a `scope int* p` in
that context, and this pointer points to the stack variable `x`.

`qux` uses `foo` to escape a pointer to the local stack variable `x`. The
delegate context is not even being referenced anymore when the UB happens.
`foo` is just a device that allows `scope`-laundering an arbitrary pointer.
`scope` pointer in, non-`scope` pointer out.

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