enable jemalloc assertions when configured to do so

[RalfJung]

This is essentially a re-submission of the functional part of #43648. I was unable to reproduce the issue I had back then, maybe something changed somewhere to no longer trigger the assertion.

Fixes #44152

[rust-highfive]

r? @alexcrichton

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[RalfJung]

@gnzlbg says nothing should have changed. I tried these settings:

# Whether or not jemalloc is built and enabled
use-jemalloc = true

# Whether or not jemalloc is built with its debug option set
debug-jemalloc = true

That should be enough to properly enable this, right? Then I did ./x.py build, and it went through all the way.

I verified that the relevant code in build.rs gets executed by making it panic.

[gnzlbg]

Yes, this change should be enough to configure jemalloc with debug assertions enabled when compiled with the debug cargo feature.

If you want to be extra sure that it is being compiled with debug assertions enabled, building it with -vv (verbose output, so that you see the output of the build.rs; no idea how to enable this via x.py) and then inspecting the output of ./configure should be enough.

This line of the output: https://travis-ci.org/jemalloc/jemalloc/jobs/408750420#L346 should contain debug : 1 (1 means enabled, 0 disabled).

[alexcrichton]

@bors: r+

Ok! Let's see if it gets past CI

[bors]

📌 Commit 872395a has been approved by alexcrichton

[bors]

⌛ Testing commit 872395a with merge 76aeeef...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 76aeeef to master...