Provide static glibc implementation in Zig

[alexrp]

This is an extension of #2879.

It's unlikely that we'd ever ship the full glibc code for static linking, partially because of license concerns, partially because some glibc subsystems call dlopen internally, and partially because the glibc source tree is frankly very bloated.

What we can do, though, is implement the glibc API surface in Zig as part of the #2879 effort. By doing so, users would be able to zig build-exe -static -lc -target ...-gnu, but without the license issues and without the caveats that usually apply when linking glibc statically, such as the internal use of dlopen.

Prior art: https://github.com/sunfishcode/mustang

[alexrp]

cc @polarathene, I imagine you might be interested in this.

[labyrinthgarden]

Hi! I’d like to help with this issue. I’ve been exploring the codebase and found that src/libs/glibc.zig is the right place to implement static glibc functions.

Before starting, I’d like to ask:

1. Are there any specific priority functions that need implementation first?
2. Is there a preferred testing approach (e.g., reuse existing tests in test/link/glibc_compat/ or add new ones)?

I’d be glad to start with a small function as a first contribution if that helps. Thanks for the guidance!

[alexrp]

I think we need to get quite a bit further along with #2879 before tackling the project of implementing a static glibc replacement. So if you're interested in this general area, I'd recommend contributing to #2879 for now. There are instructions for contributing on that issue, and you can check some of the linked pull requests for contribution examples.