Fix a breaking change in #30523

[ubsan]

Fix a breaking change in #30523

While this does fix a breaking change, it is also, technically, a
[breaking-change] to go back to our original way

[rust-highfive]

r? @nikomatsakis

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[solson]

Note, this was discovered in #30713.

[eddyb]

@bors r+ p=1

[bors]

📌 Commit 14e1e2a has been approved by eddyb

[bors]

⌛️ Testing commit 14e1e2a with merge e5817d0...

[bors]

💔 Test failed - auto-linux-32-opt

[SimonSapin]

command timed out: 1200 seconds without output running ['make', 'check'], attempting to kill

[pnkfelix]

@bors retry

[GuillaumeGomez]

It would be nice to add test which failed with the new version, no?

[bors]

⌛️ Testing commit 14e1e2a with merge 21b025f...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt

[nikomatsakis]

It would be good to have a test case, I agree.