As helper unmaps 64-bit vDSO blob, it can call only raw syscalls.
Also by that reason it's code should be not instrumented with GCOV/ASAN.
Disable instrumentation by separating it into new object and filtering
gcov/asan cflags.

Fixes: #290
@avagin, it rarely reproduces, I failed to reproduce even once
(with gcov, on the same env00 test, with the same linux-next)
please, reopen #290 if you'll spot it afterward.
Reported-by: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>