CMake: Update autorestart's CMakeLists to match the COMPILE_DEFINITIONS (rather than add_definitions) of the other components' CMakeLists files.

direct/src/autorestart/CMakeLists.txt

@@ -1,3 +1,3 @@
-add_definitions(-DWITHIN_PANDA)
 add_executable(autorestart autorestart.c)
+set_target_properties(autorestart PROPERTIES COMPILE_DEFINITIONS WITHIN_PANDA)
 target_link_libraries(autorestart p3dtool)