python312Packages.libvirt: fix cross build (#370623)

pkgs/development/python-modules/libvirt/default.nix

···
 {
+  stdenv,
   lib,
   buildPythonPackage,
   fetchFromGitLab,
···
     rev = "v${version}";
     hash = "sha256-zOjTGXwxjd6QT01AaIln0FdP/8UZS0W3yPltUhlocpk=";
   };
+
+  postPatch = ''
+    substituteInPlace setup.py \
+      --replace-fail 'pkg-config' "${stdenv.cc.targetPrefix}pkg-config"
+  '';
 
   build-system = [ setuptools ];