qt5.qtwebkit: Fix paths in pc files

In be1b22538a,
CMake setup-hook started to respect setOutputFlags. Since qtModule disables it by default,
cmake no longer received the multiple-output adjusted installation directory flags when
building the qtwebkit package. This resulted in incorrect paths in generated pkg-config files
and CMake config files.

Let’s temporarily enable setOutputFlags in the qtwebkit expression, until the commit is reverted.

pkgs/development/libraries/qt-5/modules/qtwebkit.nix

@@ -34,6 +34,9 @@ qtModule {
     bison flex gdb gperf perl pkgconfig python2 ruby
   ] ++ optional usingAnnulenWebkitFork cmake;
 
+  # Temporary fix for https://github.com/NixOS/nixpkgs/commit/be1b22538a60e52987d238bb11f93043682b6e9a
+  setOutputFlags = true;
+
   cmakeFlags = optionals usingAnnulenWebkitFork ([ "-DPORT=Qt" ]
     ++ optionals stdenv.isDarwin [
       "-DQt5Multimedia_DIR=${getDev qtmultimedia}/lib/cmake/Qt5Multimedia"