xwayland: don't fail on SIGCHLD
SIGCHLD here isn't fatal: we have other means of notifying that things were successful or failure, and it causes many compositors to have to do a bunch of extra work:
https://github.com/qtile/qtile/issues/5101 https://github.com/flacjacket/pywlroots/pull/207#issuecomment-2502680133 https://github.com/djpohly/dwl/pull/212
Signed-off-by: Tycho Andersen tycho@tycho.pizza