Added support for boards with only private overlays.

chromeos/scripts/build_packages

 #!/bin/bash
 PROG=$(basename $0)
 
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Script to build the set of binary packages needed by Chrome OS. It will
 # cross compile all of the packages into the given targets root and build
 # binary packages as a side-effect. The output packages will be picked up
@@ skipping 92 matching lines @@
     # without the jobs flag.
     FLAGS_retries=1
   fi
 fi
 
 if [[ "${FLAGS_withdebug}" -eq "${FLAGS_FALSE}" ]]; then
   export USE="${USE} -cros-debug"
 fi
 
 BOARD=$(echo "${FLAGS_board}" |cut -d '_' -f 1)
-BOARD_OVERLAY="${SRC_ROOT}/overlays/overlay-${BOARD}"
+BOARD_OVERLAY=$($SCRIPTS_DIR/bin/cros_overlay_list \
+  --board "$BOARD" \
+  --primary_only)
 TC_ARCH=$(awk -F'-' '{ print $1 }' < "${BOARD_OVERLAY}/toolchain.conf")
 case "${TC_ARCH}" in
   arm*)
     ARCH="arm"
     ;;
   *86)
     ARCH="x86"
     ;;
   *)
     error "Unable to determine ARCH from toolchain: ${FLAGS_board}"
@@ skipping 120 matching lines @@
 
     # Update the remainder of the packages.
     eretry ${EMERGE_BOARD_CMD} -uDNv ${EMERGE_FLAGS} ${PACKAGES}
   fi
 fi
 
 
 echo "Builds complete"
 print_time_elapsed
 echo "Done"