If you build on a system with git < 2.14 from scratch (e.g. debian9), the
tree will be marked as "dirty" and the version will include "-dirty", leading
to a reproducibility problem. The issue is the inode count for Licnses/README
changing due to do_populate_lic hardlinking a copy of the file. We avoid
this by ensuring the index is updated with a "git diff" before the
u-boot machinery tries to determine the version.
