Update git submodules

* Update prebuilts/build-tools from branch 'master'
  to 2a0a6e85f50636eaae93431933d64e9a921c4a64
  - Merge "Add symlinks for egrep(1) and grep(1)."
  - Add symlinks for egrep(1) and grep(1).
    
    Test: treehugger
    Change-Id: I20cf6066b9a48775c31729b6731ff5e474d70859
    
1 file changed