Check for occupied niches

[saethlin]

This is a replacement for #104862

r? @ghost

[bors]

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[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

#16 2.671 Building wheels for collected packages: reuse
#16 2.672   Building wheel for reuse (pyproject.toml): started
#16 2.917   Building wheel for reuse (pyproject.toml): finished with status 'done'
#16 2.918   Created wheel for reuse: filename=reuse-4.0.3-cp310-cp310-manylinux_2_35_x86_64.whl size=132715 sha256=dfa09868353292d98f811d3efdb0d54d07389e808efc71d68e3b93c514bf8bec
#16 2.918   Stored in directory: /tmp/pip-ephem-wheel-cache-j9jz1gq4/wheels/3d/8d/0a/e0fc6aba4494b28a967ab5eaf951c121d9c677958714e34532
#16 2.921 Installing collected packages: boolean-py, binaryornot, tomlkit, reuse, python-debian, markupsafe, license-expression, jinja2, chardet, attrs
#16 3.316 Successfully installed attrs-23.2.0 binaryornot-0.4.4 boolean-py-4.0 chardet-5.2.0 jinja2-3.1.4 license-expression-30.3.0 markupsafe-2.1.5 python-debian-0.1.49 reuse-4.0.3 tomlkit-0.13.0
#16 3.316 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#16 DONE 3.4s
---
     |
note: function defined here
    --> compiler/rustc_monomorphize/src/collector.rs:939:4
     |
939  | fn should_codegen_locally<'tcx>(tcx: TyCtxtAt<'tcx>, instance: Instance<'tcx>) -> bool {

For more information about this error, try `rustc --explain E0308`.
error: could not compile `rustc_monomorphize` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...

[bors]

☔ The latest upstream changes (presumably #121614) made this pull request unmergeable. Please resolve the merge conflicts.