CMake: Use file(GENERATE) to write the 'data' file

… when available.

Fixes warning:
Policy CMP0026 is not set: Disallow use of the LOCATION target property.

See: bug #694

CMakeLists.txt

@@ -1480,12 +1480,17 @@ install(DIRECTORY data/core/ DESTINATION "${INSTALL_DATADIR}")
 # Also tell arx where to find the not yet installed data
 # This is required to run arx from the build directory without installing
 set(arx_core_dir "${CMAKE_SOURCE_DIR}/data/core")
-foreach(config IN LISTS CMAKE_CONFIGURATION_TYPES CMAKE_BUILD_TYPE)
-	get_property(arx_location TARGET arx PROPERTY LOCATION_${config})
-	get_filename_component(arx_location "${arx_location}" PATH)
-	file(RELATIVE_PATH arx_core_dir_rel "${arx_location}" "${arx_core_dir}")
-	file(WRITE "${arx_location}/data" "${arx_core_dir_rel}\n")
-endforeach()
+get_filename_component(arx_core_dir "${arx_core_dir}" ABSOLUTE)
+file(TO_NATIVE_PATH "${arx_core_dir}" arx_core_dir)
+if(CMAKE_VERSION VERSION_LESS 2.8.12)
+	foreach(config IN LISTS CMAKE_CONFIGURATION_TYPES CMAKE_BUILD_TYPE)
+		get_property(arx_location TARGET arx PROPERTY LOCATION_${config})
+		get_filename_component(arx_location "${arx_location}" PATH)
+		file(WRITE "${arx_location}/data" "${arx_core_dir}\n")
+	endforeach()
+else()
+	file(GENERATE OUTPUT "$<TARGET_FILE_DIR:arx>/data" CONTENT "${arx_core_dir}\n")
+endif()
 
 # Install the data install script
 if(INSTALL_SCRIPTS AND NOT WIN32)