For Zig Version 0.11.0 and Godot 3.2.0+
Before you use this as a package, you must generate the GDNative and class files for Zig, this is done by bulding with the following options
zig build -Dgdnative="mydir/gdnative_api.json" -Dclasses="mydir/api.json"
These options correspond to the files that are found in Godot's GDNative, which you can get here
The "test_example" folder contains an explained minimal example of how to use this as a package, with the build script, library entry point and a sample class included that can be built with
zig build