base_image_util.sh: Temporarily disable 32-bit runtime on aarch64

Disable before new libc++ prebuilts are available.
Revert once chromiumos-sdk succeeds.

BUG=b:204093890
TEST=CQ

Change-Id: I759e2d8d1c506b1b600e8292d2e7f4e2b6d55e13
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3567537
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Auto-Submit: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
1 file changed