Add support for older GLIBC versions and musl targets to improve Linux compatibility

[luckzylp]

Problem / Background

The current Linux binaries require a recent GLIBC version (GLIBC_2.39 or higher), which makes them incompatible with many older or long-term-support systems, such as:

• Ubuntu 16.04 (Xenial) — ships with GLIBC 2.23
• Ubuntu 20.04 (Noble) — ships with GLIBC 2.31
• Ubuntu 22.04 (Jammy) — ships with GLIBC 2.35
• CentOS 7 / RHEL 7 derivatives (GLIBC 2.17)
• Many minimal Docker base images and legacy environments

Example error when running on Ubuntu 16.04:

./csharp-language-server: /lib/x86_64-linux-gnu/libm.so.6: version `GLIBC_2.29' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.25' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.27' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.28' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.29' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.30' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.33' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.34' not found (required by ./csharp-language-server)
./csharp-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.39' not found (required by ./csharp-language-server)

I raised a PR #248 to add support for this requirement.

[SofusA]

I am a little hesitant on this. I prefer not to have too many dependencies.
I think support for older versions of Ubuntu might be more suited in a ppa.

[luckzylp]

First of all, I want to say this is a really great project — thank you for the
work you’ve put into it.

The motivation behind this PR is simply to let the project benefit a wider range
of Linux deployments, especially environments that are still very common in
production but ship with older glibc versions.

To clarify the scope of this change:

• This PR does not introduce any additional runtime dependencies.
• The only new dependency is zig, and it is used exclusively in CI/CD for
  building an additional Linux-compatible binary.
• It does not change the existing build targets or affect current users in
  any way.
• It also does not imply or require long-term maintenance or official support
  for any specific Linux distribution.

The intention is simply to provide users with one more optional choice, not to
expand the project’s support or maintenance commitments.

If there’s a preferred way to scope or present this (e.g. marking it as optional
or compatibility-focused), I’m very happy to adjust the PR accordingly.