x86/build: generate syscalls-{64,32}.built-in.o

After uncommenting FIXME:
It will add sc_exec_table_32 for compatible tasks to sys-exec-tbl.c

Now it does:
 - add two different 32/64 syscall tables for cr-exec
   sys-exec-tbl-{64,32}.
 - add two different syscall headers syscall-{64,32}.h,
   that are included from more x86 generic syscall.h depending
   on -DCONFIG_X86_{32,64} option.
 - builds two different syscalls-{32,64}.built-in.o
 - for criu core files, that need SYS_memfd_create and other
   SYS_* __NR_* defines (currently kerndat.c and shmem.c),
   create simple syscall-codes.h that includes syscall-codes-64.h
   [Added after rebase on master]

That way after apply, the compatible patch set will be simply
able to bisect for regressions.

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