`build.zig` uses `optimize == .ReleaseSafe` check deprecated in newer 0.17.0-dev builds

[sloanev]

I'm not sure if keeping up with breaking changes in Zig is a priority here. If so, I got this build error on zig 0.17.0-dev.1476+91a29d707:

[...]/build.zig:748:38: error: no field named 'ReleaseSmall' in enum 'lang.Optimize'
        .CONFIG_SMALL = optimize == .ReleaseSmall,

This is broken in any builds since https://codeberg.org/ziglang/zig/commit/ae4e835a662a3b8c512511b87f4a44065e26dbb7