[cmake] Simplify - dictionary options come only from here.

core/CMakeLists.txt

@@ -27,17 +27,17 @@ endif()
 if(UNIX)
   add_subdirectory(unix)
   set(unix_objects $<TARGET_OBJECTS:Unix>)
-  set(dict_opts -DSYSTEM_TYPE_unix ${dict_opts})
+  set(dict_opts -DSYSTEM_TYPE_unix)
 endif()
 if(WIN32)
   add_subdirectory(winnt)
   set(winnt_objects $<TARGET_OBJECTS:Winnt>)
-  set(dict_opts -DSYSTEM_TYPE_winnt ${dict_opts})
+  set(dict_opts -DSYSTEM_TYPE_winnt)
 endif()
 if(cocoa)
   add_subdirectory(macosx)
   set(macosx_objects $<TARGET_OBJECTS:Macosx>)
-  set(dict_opts -DSYSTEM_TYPE_macosx ${dict_opts})
+  set(dict_opts -DSYSTEM_TYPE_macosx)
 endif()
 
 set(CORE_OS_DICT_CXX_FLAGS ${dict_opts} PARENT_SCOPE)