bug#26180: Remove motif toolkit support

[Po Lu]

Glenn Morris <rgm@gnu.org> writes:

> Package: emacs
> Version: 25.2
> Severity: wishlist

We agreed to keep Motif support in a discussion last December, so I'm
closing this bug.

I agree with Martin in that there isn't a single concrete case where
Motif interferes with the development of a feature.  Most of the
important code is shared with the Lucid/Athena build, since both
toolkits use Xt, and the toolkit that causes us difficulties is
typically GTK 3.  For instance, it's the only toolkit that has to be
special-cased for frame resize synchronization, since it doesn't behave
well when it doesn't know about the basic frame counter, while the
development of that feature went smoothly on every other build we
currently support.