Enable Unity Builds unconditionally

Projects using KDDW won't need to modify KDDW, so there's no impact
on incremental builds

CMakeLists.txt

@@ -82,6 +82,12 @@ include(FeatureSummary)
 option(${PROJECT_NAME}_QT6 "Build against Qt 6" OFF)
 option(${PROJECT_NAME}_DEVELOPER_MODE "Developer Mode" OFF)
 option(${PROJECT_NAME}_PYTHON_BINDINGS "Build python bindings" OFF)
+
+if(${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.16.0")
+  option(${PROJECT_NAME}_UNITY_BUILD "Build with CMake's UNITY_BUILD" ON)
+endif()
+
+
 if(${PROJECT_NAME}_PYTHON_BINDINGS AND (CMAKE_BUILD_TYPE MATCHES "^[Dd]eb" OR ${PROJECT_NAME}_STATIC))
   message(FATAL_ERROR "** Python Bindings are disabled in debug or static builds.")
 endif()
@@ -225,3 +231,8 @@ endif()
 if(${PROJECT_NAME}_DOCS)
   add_subdirectory(docs) # needs to go last, in case there are build source files
 endif()
+
+if (${PROJECT_NAME}_UNITY_BUILD)
+  set_target_properties(kddockwidgets PROPERTIES UNITY_BUILD ON)
+  set_target_properties(kddockwidgets_multisplitter PROPERTIES UNITY_BUILD ON)
+endif()

src/CMakeLists.txt

@@ -242,7 +242,6 @@ install(FILES "${CMAKE_CURRENT_BINARY_DIR}/KDDockWidgetsConfig.cmake"
 if(${PROJECT_NAME}_DEVELOPER_MODE)
   # Under developer mode since kddw might be a sub-folder of a project setting a different value for QT_DISABLE_DEPRECATED_BEFORE
   target_compile_definitions(kddockwidgets PRIVATE QT_DISABLE_DEPRECATED_BEFORE=0x060000)
-  set_target_properties(kddockwidgets PROPERTIES UNITY_BUILD ON)
 
   if (NOT ${PROJECT_NAME}_QTQUICK) # TODO: We can support it
     add_executable(kddockwidgets_linter layoutlinter_main.cpp)

src/private/multisplitter/CMakeLists.txt

@@ -73,8 +73,6 @@ if(${PROJECT_NAME}_DEVELOPER_MODE)
   # Under developer mode since kddw might be a sub-folder of a project setting a different value for QT_DISABLE_DEPRECATED_BEFORE
   target_compile_definitions(kddockwidgets_multisplitter PRIVATE QT_DISABLE_DEPRECATED_BEFORE=0x060000)
 
-  set_target_properties(kddockwidgets_multisplitter PROPERTIES UNITY_BUILD ON)
-
   if(${PROJECT_NAME}_TESTS AND NOT ${PROJECT_NAME}_QTQUICK)
     add_subdirectory(tests)
   endif()