build_abi: add options to help maintaining the abi.xml

Add the options
  -u | --update         Update the abi.xml in the source directory
  -n | --nodiff         Do not generate a ABI report with abidiff
  -r | --print-report   Print ABI report in case of differences

This allows the following example usages (besides others):

  - Update the ABI and print the reported differences
    That is useful to take the report for the commit message when
    updating the abi.xml.
     $ build/build_abi.sh -r -u

  - Update the ABI and ignore any difference
    If you are not interested in the report or any existing difference,
    but just want to update the abi.xml.
     $ build/build_abi.sh -u -n

Change-Id: Ifc97b7043da6e93b90e670bab2f89796aff655ac
Signed-off-by: Matthias Maennich <maennich@google.com>
2 files changed