It's used in restorer to map compatible vDSO blob.
When !CONFIG_COMPAT it's not needed and even more:
vdso_fill_symtable_compat is macro and is undefined in that
case. It will never shoot, as compat_vdso is always false
for that case, but get rid of it.
  I also need to leave CONFIG_X86_64 here, as arch_prctl()
is not defined for x86_32.

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>