Update git submodules

* Update kernel/build from branch 'master'
  to b39bd329b3fb776864c2f618a81b3902d3f73397
  - gki: compare_mixed_trees: Correctly strip source dir
    
    Clean up from original introduction of compare_mixed_trees:
    
     - os.sep instead of os.pathsep
     - Only consider compiled files that start with src_dir_prefix
     - Sort gki_files output alphabetically
    
    Fixes: c93827a5267c ("compare_mixed_trees: Add script to compare mixed tree sources")
    Change-Id: Ife12cb59123d3ba90df68e0663743abd48f9b7f6
    Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>