UPDATE 08/4/2015

Vivaldi is avalaible in portage, so all You have to do:

emerge --sync
emerge -av vivaldi

ln -s /usr/lib64/libudev.so.1 /usr/lib64/libudev.so.0
FEATURES="-strict"  emerge -av vivaldi
chown root:root /opt/vivaldi/vivaldi-sandbox
chmod 4755 /opt/vivaldi/vivaldi-sandbox