dnsmasq: fix cross-compilation

This is done by specifying pkg-config in the makeFlags, ensuring that
the correct pkg-config is injected.

Depends on changes that are currently only in staging:

- 07ecf87693fec1032c19ba1f5b41dc9cf260abb2
- 4f6ec19dbc322d7ce8df9108b76e0db79682353e

See https://github.com/NixOS/nixpkgs/pull/114902 for those changes.

pkgs/tools/networking/dnsmasq/default.nix

@@ -1,5 +1,5 @@
 { lib, stdenv, fetchurl, pkg-config, dbus, nettle, fetchpatch
-, libidn, libnetfilter_conntrack }:
+, libidn, libnetfilter_conntrack, buildPackages }:
 
 with lib;
 let
@@ -33,6 +33,7 @@ stdenv.mkDerivation rec {
     "BINDIR=$(out)/bin"
     "MANDIR=$(out)/man"
     "LOCALEDIR=$(out)/share/locale"
+    "PKG_CONFIG=${buildPackages.pkg-config}/bin/${buildPackages.pkg-config.targetPrefix}pkg-config"
   ];
 
   hardeningEnable = [ "pie" ];