Roll Chromite from 39fbb307bc9a to 12c6d67a4298 (2 revisions)

https://chromium.googlesource.com/chromiumos/chromite.git/+log/39fbb307bc9a..12c6d67a4298

2020-08-15 vapier@chromium.org sysroot_lib: add arm64-generic prebuilt fallback for arm64
2020-08-14 mikenichols@chromium.org chromeos_config: Move the oldest branch to trigger only from uprev

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/chromite-chromium-autoroll
Please CC chrome-os-gardeners@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

Cq-Include-Trybots: luci.chrome.try:chromeos-betty-pi-arc-chrome;luci.chromium.try:chromeos-kevin-rel
Tbr: chrome-os-gardeners@google.com
Change-Id: Ic130b52bd20a44f4b15ddebbfddec5043a1440c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2360250Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#798695}

DEPS

@@ -875,7 +875,7 @@ deps = {
 
   # Build tools for Chrome OS.
   'src/third_party/chromite': {
-      'url': Var('chromium_git') + '/chromiumos/chromite.git' + '@' + '39fbb307bc9a3f044427d0bdafafe45d4b12a040',
+      'url': Var('chromium_git') + '/chromiumos/chromite.git' + '@' + '12c6d67a42982a73417a0aa289244be2c5d350fe',
       'condition': 'checkout_chromeos',
   },