> The symptom is: after starting an emacs frame (and a server) under
DISPLAY=:0, in a different DISPLAY environment, either in :0.1 (local) or
:10.0 (via ssh), when I run emacsclient -c to start a new frame, emacs
crashes due to a floating point exception.
> The crash does not occur when running emacs -Q.  A minimal init.el is
attached to regenerate the crash.

Let me add one more piece of info:
If I run emacsclient -c under the same DISPLAY=:0, the crash does NOT occur
and a second frame shows up correctly.