We presently don't package isl. Unfortunately, if the host is already
using gcc-5.2 (as is presently the case on Arch Linux), configure will
autodetect the host's libisl, and do_compile will break because the
system isl headers aren't pulled in. In lieu of packaging isl, disable
it for now.
[YOCTO #8376]
Signed-off-by: Richard Tollerton <rich.tollerton@ni.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
