The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/fea61e4043104625c45a011f804fa068af21896c

commit fea61e4043104625c45a011f804fa068af21896c
Author: Simon Glass <sjg@chromium.org>
Date: Sat Dec 01 05:01:28 2018

u-boot: Make warnings-as-errors optional

It is a pain to have minor warnings break an ebuild run. Provide a USE
flag to disable this behaviour.

BUG=chromium:908228
TEST=USE="-werror emerge-grunt u-boot"
See that warnings don't stop the build

Change-Id: I4dd5c52b2356faba8754ded07b634c8031f668d2
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1350222
Reviewed-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[modify] https://crrev.com/fea61e4043104625c45a011f804fa068af21896c/sys-boot/u-boot/u-boot-9999.ebuild

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/cc78a7b74f8efac0906257dcab7374514df6118a

commit cc78a7b74f8efac0906257dcab7374514df6118a
Author: Simon Glass <sjg@chromium.org>
Date: Wed Dec 19 05:33:27 2018

u-boot: Add support for building sandbox

U-Boot's sandbox is a convenient way to build and test vboot
functionality. Add a USE flag to build this. This requires SDL so add that
to the sdk.

This works by building using the chromeos_sandbox target, using the host
toolchain (not cross-compiled). The resulting output is U-Boot along with
SPL and TPL. There is also a fully ready Chromium OS firmware image which
is installed, for testing purposes.

Instructions for running the result are in the ebuild.

The USE_STDINT option is not needed with vboot anymore, so drop it.

BUG=chromium:908228
TEST=USE="sandbox vboot" sudo -E emerge u-boot
See that it builds OK
Follow instructions at the top of the ebuild to run U-Boot inside and
outside the chroot.

Change-Id: Iaffe6d4ccccc2514cf6efbb793356eef2973a2b2
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1350223
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[modify] https://crrev.com/cc78a7b74f8efac0906257dcab7374514df6118a/sys-boot/u-boot/u-boot-9999.ebuild