Merge change 5150 into donut

* changes:
  don't fail if no required bootloaders are defined
tree: dbf9cd693c7756607d6dff8c918fc91f188f4aef
  1. core/
  2. libs/
  3. target/
  4. tools/
  5. buildspec.mk.default
  6. cleanspec.mk
  7. envsetup.sh