qt6: Use only one CMake option for Qt6

We still had OPTION_QT6 leftovers

CMakeLists.txt

@@ -98,7 +98,7 @@ endif()
 
 #option(${PROJECT_NAME}_QTQUICK "Build for QtQuick instead of QtWidgets" OFF)
 
-if (OPTION_QT6)
+if (${PROJECT_NAME}_QT6)
   find_package(Qt6Widgets REQUIRED)
   find_package(Qt6Test REQUIRED)
   set(QT_MAJOR_VERSION 6)
@@ -123,7 +123,7 @@ include(QtInstallPaths) #to set QT_INSTALL_FOO variables
 macro(set_compiler_flags targetName)
   if(${PROJECT_NAME}_DEVELOPER_MODE)
     target_compile_definitions(${targetName} PUBLIC DOCKS_DEVELOPER_MODE PRIVATE QT_FORCE_ASSERTS)
-    if(NOT MSVC AND NOT OPTION_QT6) # We're not warnings clean with Qt6 yet
+    if(NOT MSVC AND NOT ${PROJECT_NAME}_QT6) # We're not warnings clean with Qt6 yet
       target_compile_options(${targetName} PRIVATE -Wall -Wextra -Werror -Wno-error=deprecated-declarations)
       if (APPLE)
         target_compile_options(${targetName} PRIVATE -Wweak-vtables)

src/CMakeLists.txt

@@ -178,7 +178,7 @@ endif()
 
 if (WIN32)
     target_link_libraries(kddockwidgets PRIVATE Qt${QT_MAJOR_VERSION}::GuiPrivate Dwmapi)
-elseif(NOT APPLE AND NOT EMSCRIPTEN AND NOT OPTION_QT6)
+elseif(NOT APPLE AND NOT EMSCRIPTEN AND NOT ${PROJECT_NAME}_QT6)
     find_package(Qt${QT_MAJOR_VERSION}X11Extras)
     target_link_libraries(kddockwidgets PUBLIC Qt${QT_MAJOR_VERSION}::X11Extras)
 endif()