util/build_with_clang: Enable vell
util/build_with_clang: Enable vell

BRANCH=none
BUG=b:172020503
TEST=CC=clang make BOARD=vell

Signed-off-by: Tom Hughes <fc5c12f30a5ed2baa0581f44ee14ad1eb7b20d83@chromium.org>
Change-Id: I87ec7a3ce4987efb96f64b50ed6af61973881c86
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3953258
Reviewed-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec