Create 32-bit core files for 32-bit processes on 64-bit machines.
The 64-bit machine supported right now is amd64, but it's not too
hard to add powerpc64.

Obtained from:	Juniper Networks, Inc.
Fix relocations related to dpcpu and vnet sets. The address is
rebased to point to the allocated memory, but for architectures
that have non-zero relocation addends, the address comparison
happens on the "unfinalized" address.
After the addend is taken into account, call elf_relocaddr() to
make sure we rebase properly.