qt5: win: use qtwebkit by default

use -DBUILD_QT5_WEBKIT=OFF to disable qtwebkit for qt5

CMakeLists.txt

@@ -162,6 +162,7 @@ endif(MSVC)
 
 # Switch to build FreeCAD with Qt5
 OPTION(BUILD_QT5 "Build with Qt5." OFF)
+OPTION(BUILD_QT5_WEBKIT "Build with Qt5." ON)
 OPTION(BUILD_GUI "Build FreeCAD Gui. Otherwise you have only the command line and the Python import module." ON)
 OPTION(FREECAD_MAINTAINERS_BUILD "Build FreeCAD for Maintainers, with Docu and 3rd party libs. On Windows the Installer is build." OFF)
 OPTION(FREECAD_USE_EXTERNAL_ZIPIOS "Use system installed zipios++ instead of the bundled." OFF)
@@ -802,9 +803,8 @@ endif(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
             find_package(Qt5UiTools)
             find_package(Qt5Network)
             find_package(Qt5Concurrent)
-            if (NOT WIN32)
-            # Disable for Windows for now since building the Qt sources always fails
-            find_package(Qt5WebKitWidgets)
+            if (BUILD_QT5_WEBKIT)
+                find_package(Qt5WebKitWidgets)
             endif()
         endif(BUILD_GUI)