This is libffi, packaged for Zig.
First, update your build.zig.zon:
# Initialize a `zig build` project if you haven't already
zig init
zig fetch --save git+https://github.com/allyourcodebase/libffi.git
You can then import libffi in your build.zig with:
const libffi = b.dependency("libffi", .{
.target = target,
.optimize = optimize,
});
exe.root_module.linkLibrary(libffi.artifact("ffi"));