Add tests for checking the glibc version required by rustc

[Kobzol]

We promise that our GNU rustc toolchains won't need a glibc newer than a certain version (https://blog.rust-lang.org/2022/08/01/Increasing-glibc-kernel-requirements.html), but we don't currently have a test that would actually test this. It can be quite easy to inadvertedly bump the glibc, for example when updating base images of the OS in a container that builds the dist toolchain on CI.

It would be nice of we had some kind of (run-make?) test that checks the exact version of glibc used by a toolchain compiled on CI. It should be executed explicitly in specific CI runners, so that we can vary the required glibc version per CI job (and thus per tier/platform).