How to cross-compile in the "new" Zig master?

Check out the Upgrade Guide here: Move many settings from being per-Compilation to being per-Module by andrewrk · Pull Request #18160 · ziglang/zig · GitHub

In summary, I think you should use something like this:

const target = b.resolveTargetQuery(.{
    .cpu_arch = .x86_64,
    .os_tag = .uefi,

Then you can pass target to addExecutable and friends.