Add script to build clang-tools. am: ea86c04e26 am: d0e3a1b5c8
am: 0754648f0e

Change-Id: I0787af9697adbe7885d8c654553de719fcce302b
tree: cd1964604b5fb5e9e00d62f226bf27897d188378
  1. build-prebuilts.sh