Update build-tools to ab/4051621 am: f28fb1e5f6  -s ours
am: d8184e3a36  -s ours

Change-Id: I3a0e6614199aaec55ca89d057484550040ddfd2a
tree: 99e76231fab7582e6952ca8dc170d04f857822de
  1. darwin-x86/
  2. linux-x86/
  3. build-prebuilts.sh
  4. manifest.xml