compel hgen: fix for 32-bit ARM

Since commit 93db22b ("compel: no -r for ARM ldflags") and
commit ce043d3 ("compel: make plugins .a archives") the generated
parasite/restorer blobs for 32-bit ARM are no longer relocatable,
and so their ELF header has e_type of ET_EXEC (rather than ET_REL).
As a result, we have "Unsupported header detected" message and
a failure from compel hgen.

This commit allows e_type == ET_EXEC in case NO_RELOCS is defined.
I am not sure if it's OK to still allow ET_REL -- maybe Dmitry
can chime in on that.

Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>