Build `*-unknown-linux-gnu` binaries with old glibc for portability

[xtqqczze]

Platform	Kernel	glibc
*-unknown-linux-gnu 1	3.2	2.17
ubuntu-22.04	5.15	2.35
ubuntu-24.04	6.8	2.39
ubuntu-26.04	7.0	2.43

We could use Ubuntu 22.04 in CI to link against an oldish glibc version.

[oech3]

Strongly disagree for performance. We already have musl binary. Please close this issue soon.

[oech3]

But I'm OK to include output of libc.so.6 --version | head -n 1.

[xtqqczze]

We should prioritize shipping binaries that actually run on supported platforms, which we cannot guarantee if they’re linked against a newer glibc than the target system provides.

For example, such binaries may fail on Ubuntu 22.04, which remains under standard support until April 2027.

[oech3]

It is why we have musl. No need to change glibc binary.

[xtqqczze]

Perhaps we should consider discontinuing the GNU-linked binaries entirely. Users who specifically need them can install them through their package manager or build from source.

[oech3]

Unfortunately, static musl binary cannot support stdbuf. So we cannot reduce to one target.

[xtqqczze]

We also have latest-commit binaries.

[oech3]

latest-commit is coming from same CICD.yml workflow. So nothing we should especially care about it (though release build for all unmerged PRs is overkill for me).

[xtqqczze]

I also don’t think we want *-unknown-linux-gnu binaries to effectively require glibc 2.43 once ubuntu-latest on GitHub-hosted runners moves to 26.04, so we should address this before that happens.

[oech3]

We should fix (lib)stdbuf instead of dropping glibc version.

[oech3]

Oh, I was missing that there is nothing we can LD_PRELOAD to musl binary. So actually nothing to fix.

[oech3]

In my opinion, people want to use latest stdbuf should use latest Ubuntu LTS too. Also I don't think may people are interested in stdbuf.

[oech3]

We currently run GnuTests with release-small profile. If we used outdated Ubuntu at there and publish binaries, it is 0 cost.
Also GNU has some unshare tests masking /proc.