Clang doesn't accept "struct objc_object*" as synonym for "id" in Objective-C
code, so use the real "id" for it while still using the struct pointer for C++
code where "id" is not defined.
Closes#13565.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71517 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
