It appears that you're trying to install a kernel for which dkms can't build the version of the v4l2loopback kernel module that you have.
I don't see why this would affect Gnome, but if it's causing problems for the rest of the system maybe try uninstalling v4l2loopback-dkms until you can get a version that works, or else use an older kernel.
Alternately, if you're feeling brave and this is the same version that's in debian stable right now, you could edit /usr/src/v4l2loopback-0.12.7/v4l2loopback.c and replace strlcpy with strscpy in two places.