This fixes a regression introduce in d613991a8e
reported on IRC by Mathieu Othacehe <othacehe@gnu.org>.
* gnu/packages/patches/grub-cross-system-i686.patch
[GRUB_MACHINE_EFI && !__x86_64__]: Add missing .byte alternative to 64-bit
instruction.
* gnu/packages/patches/grub-cross-system-i686.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/bootloaders.scm (grub): Use it.