"CGo" is a FFI technique for Go code to call into C. My read is that they haven't transpiled any Go to C; they're compiling and linking a mixed Go+C program. And IIRC, Go on Linux makes direct syscalls rather than using libc, so the need to pin glibc versions is exclusively on the C side. That's probably why the Go folks haven't invested much effort into it. I don't know if there's anyone you could throw money at who would get glibc pinning for CGo implemented and merged.
I certainly would love to see this become equally easy in other languages / with standard toolchains. I write a lot of Rust. I have one program in particular that I'd like to make a one-binary install that works on old glibc versions. My program uses glibc both through Rust's std and through a C library (SQLite) it compiles/links in. I'd prefer to just throw a glibc version in my Cargo.toml and have cross compiling Just Work, rather building within a Docker container with an old glibc version, or having to install both Rust and Zig toolchains, or the like.
I certainly would love to see this become equally easy in other languages / with standard toolchains. I write a lot of Rust. I have one program in particular that I'd like to make a one-binary install that works on old glibc versions. My program uses glibc both through Rust's std and through a C library (SQLite) it compiles/links in. I'd prefer to just throw a glibc version in my Cargo.toml and have cross compiling Just Work, rather building within a Docker container with an old glibc version, or having to install both Rust and Zig toolchains, or the like.