http://labs.it-huset.se/jenkins/job/Emacs/job/emacs-xwidgets-mvp-merge-master/ws/xwidget-emacs-157-1.x86_64.rpm
its built by jenkins, and the recipy looks like:
git fetch
git merge origin/master
./autogen.sh
./configure --with-xwidgets --with-x-toolkit=gtk3
make -j4 bootstrap
mkdir -p installdir
make install DESTDIR=installdir
/usr/local/bin/fpm -s dir -t rpm -n xwidget-emacs -v $BUILD_NUMBER -C
installdir usr
It would be nice if someone could try it out, but please note that its a
binary package and I cant guarantee its integrity.