* gnu/packages/patches/grub-hurd64.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/bootloaders.scm (grub)[arguments]: When building for the 64bit
Hurd, use it in new "apply-hurd64-patch" stage.
Change-Id: I780f6a92418b49e5fe0d23eb1c90e155216f1428