This reverts commit 85b468262e "Remove unused liblockdep packaging"
and 87d08943da "liblockdep: Stop trying to build packages, as it
failed to build again", but doesn't restore the patches. All our
patches, and further build fixes, were applied upstream as of
v4.13-rc1.
liblockdep is in fairly bad shape - one patch needed to make it build
at all, another to make it build in a separate directory successfully,
and a third to fix the soname. And the install rule doesn't install
its public headers. But maybe it will be useful.