build_packages: Force rebuild chromeos-config.

Force rebuilding chromeos-base/chromeos-config to prevent the
use of stale configs.

BUG=chromium:1051535
TEST=./build_packages --board=lakitu
TEST=./build_packages --board=dedede
TEST=./build_packages --board=octopus

Change-Id: Ia8d9d5f9bfafbda1d985b4d78cd47640e3dcc3e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2052216
Tested-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Mathew King <mathewk@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Mathew King <mathewk@chromium.org>
diff --git a/build_packages b/build_packages
index e477a39..eb8c876 100755
--- a/build_packages
+++ b/build_packages
@@ -240,7 +240,9 @@
 
 # Figure out which packages we should be building.
 PACKAGES=( "$@" )
-FORCE_LOCAL_BUILD_PKGS=()
+# Force rebuild chromeos-config because it is extremely cheap, and we do not
+# want to reuse stale configs.
+FORCE_LOCAL_BUILD_PKGS=( chromeos-base/chromeos-config )
 if [[ $# -eq 0 ]]; then
   PACKAGES=( virtual/target-os )
   if [[ "${FLAGS_withdev}" -eq "${FLAGS_TRUE}" ]]; then