add cmake option to use Qt or native file dialogs

CMakeLists.txt

@@ -170,6 +170,11 @@ OPTION(FREECAD_USE_EXTERNAL_SMESH "Use system installed smesh instead of the bun
 OPTION(FREECAD_USE_EXTERNAL_KDL "Use system installed orocos-kdl instead of the bundled." OFF)
 OPTION(FREECAD_USE_FREETYPE "Builds the features using FreeType libs" ON)
 OPTION(FREECAD_BUILD_DEBIAN "Prepare for a build of a Debian package" OFF)
+if (WIN32 OR APPLE)
+    OPTION(FREECAD_USE_QT_FILEDIALOG "Use Qt's file dialog instead of the native one." OFF)
+else()
+    OPTION(FREECAD_USE_QT_FILEDIALOG "Use Qt's file dialog instead of the native one." ON)
+endif()
 
 # https://blog.kitware.com/constraining-values-with-comboboxes-in-cmake-cmake-gui/
 set(FREECAD_USE_OCC_VARIANT "Community Edition"  CACHE STRING  "Official OpenCASCADE version or community edition")

src/Gui/CMakeLists.txt

@@ -1195,6 +1195,10 @@ endif(MSVC)
 
 add_library(FreeCADGui SHARED ${FreeCADGui_SRCS})
 
+if (FREECAD_USE_QT_FILEDIALOG)
+    set_source_files_properties(FileDialog.cpp PROPERTIES COMPILE_FLAGS -DUSE_QT_FILEDIALOG)
+endif()
+
 target_link_libraries(FreeCADGui ${FreeCADGui_LIBS})
 
 SET_BIN_DIR(FreeCADGui FreeCADGui)

src/Gui/FileDialog.cpp

@@ -48,10 +48,6 @@
 
 using namespace Gui;
 
-#if defined(FC_OS_LINUX)
-#undef USE_QT_FILEDIALOG
-#endif
-
 
 /* TRANSLATOR Gui::FileDialog */