Auto merge of #1445 - JOE1994:patch-1, r=RalfJung
Auto merge of #1445 - JOE1994:patch-1, r=RalfJung

Add a case to list of 'StackedBorrows violations'

A small fix was made to libstd in rust-lang/rust#70479 (back in March).
(Miri reported UB due to Stacked Borrows violation - [link to Miri error log](https://github.com/rust-lang/miri/pull/1225#discussion_r397830221))

Thank you for reviewing :+1:

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri