[Issue 18002] assert subverts the type system with the messages that it accepts

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18002

--- Comment #3 from anonymous4 <dfj1esp02 at sneakemail.com> ---
The message is not necessarily static and immutability is only a requirement of
default druntime implementation of assert failure handler, so it should be
enough for the assert failure handler to idup the string before passing it to
AssertError constructor.

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