I don't think this DSL is finalized yet, but you can see on a linked issue what the build.zig to support @import of C looks like on nightly:

    const translate_c = b.addTranslateC(.{
        .root_source_file = b.path("src/c.h"),
        .target = target,
        .optimize = optimize,
    });
    exe.root_module.addImport("c", translate_c.createModule());

https://github.com/ziglang/zig/issues/20648