As pointed out by Andrey, arch clang tests are using gcc regardless
of CLANG=1 set in travis environment.

Frankly, I do not understand how it worked before (while being
pretty sure it worked!), but here is a way to fix it.
Reported-by: Andrey Vagin <avagin@virtuozzo.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>