Do include src/generic/animateg.cpp in wxUniv/X11 sources.

This fixes linking of the widgets sample when using wxUniv/X11.

It partially reverts the changes of r73290 which only included this file in
some selected ports instead of all of them for some reason.

Closes #15327.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74499 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775