Replace `zig` in the cross-compile process with GCC cross-compiler toolchains

[kminehart]

Basically we want to use these instead: http://musl.cc/#binaries

Upgrading to zig 0.12 doesn't work when compiling Grafana to arm64 and it's best if we're not locked into a version that isn't likely to be updated.

[hairyhenderson]

If we can accomplish https://github.com/grafana/grafana/issues/87327 then we won't need to do this as we'll be able to stop building with CGO 😉