gtkd: add dev output for propagation

pkgs/development/libraries/gtkd/default.nix

@@ -7,6 +7,8 @@ in stdenv.mkDerivation rec {
   pname = "gtkd";
   version = "3.9.0";
 
+  outputs = [ "out" "dev" ];
+
   src = fetchzip {
     url = "https://gtkd.org/Downloads/sources/GtkD-${version}.zip";
     sha256 = "12kc4s5gp6gn456d8pzhww1ggi9qbxldmcpp6855297g2x8xxy5p";
@@ -118,6 +120,15 @@ in stdenv.mkDerivation rec {
     "PKG_CONFIG=${pkgconfig}/bin/pkg-config"
   ];
 
+  # The .pc files does not declare an `includedir=`, so the multiple
+  # outputs setup hook misses this.
+  postFixup = ''
+    for pc in $dev/lib/pkgconfig/*; do
+      substituteInPlace $pc \
+        --replace "$out/include" "$dev/include"
+    done
+  '';
+
   meta = with stdenv.lib; {
     description = "D binding and OO wrapper for GTK";
     homepage = https://gtkd.org;