You want the pkg-config in nativeBuildInputs, and in build.zig use linkSystemLibrary2 with .use_pkg_config = .force
Note that your build.zig probably works even without addSystemIncludePath and pkg-config because zig has some nixpkgs specific code in the compiler which I don’t personally agree with but it’s there https://github.com/ziglang/zig/blob/master/lib/std/zig/system/NativePaths.zig#L19
Unless you use mkShellNoCC of course.