CMake: override binary output location only if none of these is set.

CMakeLists.txt

@@ -65,7 +65,7 @@ set(MAGNUMBINDINGS_CMAKE_MODULE_INSTALL_DIR share/cmake/MagnumBindings)
 # <CONFIG>/lib/magnum/importers/ instead of lib/magnum/importers/<CONFIG>. Also
 # adding this to cache, making superprojects pick that up implicitly as well,
 # without forcing them to explicitly mirror this setting.
-if(NOT DEFINED CMAKE_RUNTIME_OUTPUT_DIRECTORY)
+if(NOT DEFINED CMAKE_RUNTIME_OUTPUT_DIRECTORY AND NOT DEFINED CMAKE_LIBRARY_OUTPUT_DIRECTORY AND NOT DEFINED CMAKE_ARCHIVE_OUTPUT_DIRECTORY)
     set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/$<CONFIG>/bin CACHE PATH "" FORCE)
     set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/$<CONFIG>/lib CACHE PATH "" FORCE)
     set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/$<CONFIG>/lib CACHE PATH "" FORCE)