gtk3: only build docs on linux

pkgs/development/libraries/gtk/3.x.nix

@@ -36,6 +36,7 @@
 , wayland-protocols
 , xineramaSupport ? stdenv.isLinux
 , cupsSupport ? stdenv.isLinux
+, withGtkDoc ? stdenv.isLinux
 , cups ? null
 , AppKit
 , Cocoa
@@ -49,7 +50,7 @@ stdenv.mkDerivation rec {
   pname = "gtk+3";
   version = "3.24.12";
 
-  outputs = [ "out" "dev" "devdoc" ];
+  outputs = [ "out" "dev" ] ++ optional withGtkDoc "devdoc";
   outputBin = "dev";
 
   setupHooks = [
@@ -81,7 +82,7 @@ stdenv.mkDerivation rec {
   separateDebugInfo = stdenv.isLinux;
 
   mesonFlags = [
-    "-Dgtk_doc=true"
+    "-Dgtk_doc=${boolToString withGtkDoc}"
     "-Dtests=false"
   ];
 
@@ -109,10 +110,7 @@ stdenv.mkDerivation rec {
   '';
 
   nativeBuildInputs = [
-    docbook_xml_dtd_43
-    docbook_xsl
     gettext
-    gtk-doc
     gobject-introspection
     makeWrapper
     meson
@@ -121,6 +119,10 @@ stdenv.mkDerivation rec {
     python3
     sassc
     setupHooks
+  ] ++ optionals withGtkDoc [
+    docbook_xml_dtd_43
+    docbook_xsl
+    gtk-doc
   ];
 
   buildInputs = [