Avoid falling back to the deprecated Apple-supplied system Tcl/Tk 8.5 on macOS builds as this version is known to have many critical problems and causes Python test suite failures. This last-ditch fallback behavior was removed in Python 3.11 but is still causing problems for users and Python release testing for older security-fix-only branches like this one. With this change, building of _tkinter on macOS will be skipped if no other versions of Tcl/Tk can be found.