Fixes for being used as a subproject

* Don't use CMAKE_SOURCE_DIR, always use CMAKE_CURRENT_SOURCE_DIR
* -Werror=undef found that #if was used instead of #ifdef

docs/api/CMakeLists.txt

@@ -31,7 +31,7 @@ add_custom_command(
   OUTPUT ${DOXYGEN_OUTPUT_DIR}/qch/kddockwidgets-api.qch
   COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
   #handle a bug in doxygen where image files referred to in markdown are not copied the output
-  COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_SOURCE_DIR}/screencap.gif ${DOXYGEN_OUTPUT_DIR}/html
+  COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_SOURCE_DIR}/../../screencap.gif ${DOXYGEN_OUTPUT_DIR}/html
   DEPENDS ${_dox_deps} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
   WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
 )

src/private/WindowBeingDragged.cpp

@@ -81,7 +81,7 @@ WindowBeingDragged::WindowBeingDragged(Draggable *draggable)
     }
 }
 
-#if DOCKS_DEVELOPER_MODE
+#ifdef DOCKS_DEVELOPER_MODE
 
 // Just used by tests
 WindowBeingDragged::WindowBeingDragged(FloatingWindow *fw)

src/private/WindowBeingDragged_p.h

@@ -32,7 +32,7 @@ struct DOCKS_EXPORT_FOR_UNIT_TESTS WindowBeingDragged
 public:
     explicit WindowBeingDragged(FloatingWindow *fw, Draggable *draggable);
 
-#if DOCKS_DEVELOPER_MODE
+#ifdef DOCKS_DEVELOPER_MODE
     // For tests.
     explicit WindowBeingDragged(FloatingWindow *fw);
 #endif

src/private/multisplitter/CMakeLists.txt

@@ -94,7 +94,7 @@ endif()
 target_include_directories(kddockwidgets_multisplitter
   PUBLIC
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
-    $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/src>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/../..>
   PRIVATE
     ${CMAKE_CURRENT_SOURCE_DIR}
 )

tests/CMakeLists.txt

@@ -17,7 +17,7 @@ if(POLICY CMP0043)
   cmake_policy(SET CMP0043 NEW)
 endif()
 
-include_directories(${CMAKE_SOURCE_DIR}/src)
+include_directories(${CMAKE_CURRENT_SOURCE_DIR}/../src)
 include_directories(${CMAKE_CURRENT_BINARY_DIR})
 
 set(TESTING_SRCS utils.cpp Testing.cpp)