restorer: Workaround ASan false-positives after clone().

ASan doesn't play nicely with clone if we use current stack for
child task. ASan puts local variables on the fake stack
to catch use-after-return bug:
	https://github.com/google/sanitizers/wiki/AddressSanitizerUseAfterReturn#algorithm

So it's become easy to overflow this fake stack frame in cloned child.
We need a real stack for clone().

To workaround this we add clone_noasan() not-instrumented wrapper for
clone(). Unfortunately we can't use __attrbute__((no_sanitize_addresss))
for this because of bug in GCC > 6:
	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69863



So the only way is to put this wrapper in separate non-instrumented file.

travis-ci: success for series starting with [1/6] compel/infect: fix out-of-bounds parasite memcpy()
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>