xorg-x11-drv-nouveau has an explicit Requires on libudev. Please remove it. udev has been merged into systemd and the libudev package will exist no more. See http://lists.fedoraproject.org/pipermail/devel/2012-June/168227.html Explicit Requires on libraries are always suspicous. See http://fedoraproject.org/wiki/Packaging/Guidelines#Requires xorg-x11-drv-nouveau-0.0.16-38.20120426git174f170.fc18.src.rpm
Fixed in http://koji.fedoraproject.org/koji/taskinfo?taskID=4161535