kompare: fix build with patch

Obsolete methods were still in use when 20.08 was released.
This patch ports away from them.

pkgs/applications/kde/kompare.nix

@@ -1,7 +1,8 @@
 {
   mkDerivation, lib,
   extra-cmake-modules, kdoctools,
-  kiconthemes, kparts, ktexteditor, kwidgetsaddons, libkomparediff2
+  kiconthemes, kparts, ktexteditor, kwidgetsaddons, libkomparediff2,
+  fetchpatch
 }:
 
 mkDerivation {
@@ -11,5 +12,15 @@ mkDerivation {
   buildInputs = [
     kiconthemes kparts ktexteditor kwidgetsaddons libkomparediff2
   ];
+
+  patches = [
+    (fetchpatch {
+      # Portaway from Obsolete methods of QPrinter
+      # Part of v20.12.0
+      url = "https://invent.kde.org/sdk/kompare/-/commit/68d3eee36c48a2f44ccfd3f9e5a36311b829104b.patch";
+      sha256 = "B2i5n5cUDjCqTEF0OyTb1+LhPa5yWCnFycwijf35kwU=";
+    })
+  ];
+
   outputs = [ "out" "dev" ];
 }