compel/handle-elf.c: handle R_PPC64_REL32

When compiled with clang-3.8 on ppc, compel complains:

>   GEN      criu/pie/parasite-native-blob.h
> parasite_native_blob: Error (compel/src/lib/handle-elf-host.c:541):
> Unsupported relocation of type 26

Look into R_PPC64_REL64/R_PPC64_ADDR64 and handle 32-bit the same way.

travis-ci: success for PPC+clang compile fixes
Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>