compel: fix build break on ppc64le

This patch fix a build break on ppc64le introduced by changes in the
compel's build option.

I factorized the common CFLAGS to make easier identifying particular
flags required by some architectures.

Fixes: fef01d79f7ee ("compel: cli -- Add more flags into cflags report")
travis-ci: success for compel: fix build break on ppc64le
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>