Dump TLS with the help of SYS_get_thread_area.
Primary for 32-bit applications, but this also may be used by
mixed 64/32 bit code. I do not enable dumping for 64 bit unless
we'll meet such code, but include 3 user_desc entries of TLS
as not present in 64-bit images.
That's arguable and I may include user_descs only for compat tasks.

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>