bug#46990: 28.0.50; popup menu not navigable via arrow keys on lucid build

[martin rudalics]

> 1. make clean and make distclean
> 2. ./configure ---x-toolkit=lucid <RET>
> 3. make <RET>
> 4. src/emacs -Q <RET>
> 5. Remove menu-bar by eval (menu-bar-mode -1) <RET>
> 6. <F10>
> 7. popup menu appears
> 8. popup menu navigable via mouse but not via arrow keys.
> 9. End
>
>
>
>
>
> In GNU Emacs 28.0.50 (build 1, i686-pc-linux-gnu, X toolkit, cairo version 
1.14.8, Xaw3d scroll bars)
>   of 2021-03-07 built on bluestar
> Repository revision: 8558ecd65fc1c87345353f6352299df04280e729
> Repository branch: master
> System Description: Debian GNU/Linux 9 (stretch)
>
> Configured using:
>   'configure --with-x-toolkit=lucid'

Works here but is broken for motif.  If the breakage is recent, you will
have to bisect.

martin