While restorering compatible application on x86-64, we need
to parse 32-bit vDSO. By that reason I need _three_ compiled
object versions for util-vdso:
- for native parasite it's util-vdso.o
- for compatible parasite it's compat/util-vdso.o
- for restorer it's util-vdso.o and util-vdso-elf32.o

Note, that I can't link compat/util-vdso.o to restorer, as it's
i386 ELF which ld can't link to x86_64 ELF file.

TODO: maybe I'll need to refactor and introduce generic
CONFIG_COMPAT instead of those defined(CONFIG_X86_32).

Fixes:
  pie: 27504: vdso: Mapping compatible vDSO at 0x25000
  pie: 27504: Remap 0x7f3de3efa000->0x8048000 len 0x1000
  ...
  pie: 27504: vdso: Parsing at 0xf7776000 0xf7778000
  pie: 27504: Error (pie/util-vdso.c:87): vdso: Elf header magic mismatch
  pie: 27504: Error (pie/restorer.c:1540): Restorer fail 27504
  (00.029188) Error (cr-restore.c:988): 27504 exited, status=1
  (00.033072) Error (cr-restore.c:1870): Restoring FAILED.

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>