Be a bit more correct about segfault causality

[steveklabnik]

Fixes #30819

[rust-highfive]

r? @nikomatsakis

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[nikomatsakis]

This is actually incorrect. The cause is certainly related to a violation of some invariant that the unsafe author expected to hold, but that violation itself can occur outside of an unsafe block. @RalfJung recently wrote about exactly this in a blog post, actually: https://www.ralfj.de/blog/2016/01/09/the-scope-of-unsafe.html Perhaps just rephrasing to "you can be sure the cause is related to one of the unsafe blocks" would be good?

[steveklabnik]

Ugh, right. Thanks. Updating now with your wording.

[nikomatsakis]

@bors r+ rollup

[bors]

📌 Commit eb2343f has been approved by nikomatsakis