Auto merge of #52906 - RalfJung:jemalloc, r=alexcrichton

enable jemalloc assertions when configured to do so

This is essentially a re-submission of the functional part of https://github.com/rust-lang/rust/pull/43648. I was unable to reproduce the issue I had back then, maybe something changed somewhere to no longer trigger the assertion.

Fixes https://github.com/rust-lang/rust/issues/44152