Changes to compile signing tools on darwin

The following works from a Mac with these changes:
make Q= ARCH=arm HAVE_MACOS=1 `pwd`/build/futility/futility

Only vbutil_keyblock and vbutil_kernel have been exercised.

BUG=none
TEST='make Q= ARCH=arm HAVE_MACOS=1 `pwd`/build/futility/futility'
BRANCH=none

Signed-off-by: David Riley <davidriley@chromium.org>

Change-Id: Ie69cfee0c650d4ff96be6322083a2fea1543ee39
Reviewed-on: https://chromium-review.googlesource.com/246773
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
Tested-by: David Riley <davidriley@chromium.org>
Commit-Queue: David Riley <davidriley@chromium.org>
9 files changed