This fixes a bug whereby /dev/disk/by-{label,id} would be missing on
GuixSD (/dev/disk/by-id would still contain device-mapped partitions
though.)
Reported by Mark H Weaver <mhw@netris.org>.
* gnu/packages/linux.scm (eudev-with-blkid): New variable.
* gnu/services/base.scm (udev-service): #:udev defaults to
EUDEV-WITH-BLKID.
* gnu/system.scm (%base-packages): Replace EUDEV with EUDEV-WITH-BLKID.