Makefile changes: git describe

I have never managed to get the NDS file to have a git commit hash with your Makefile. Near the end of each build, I would get this message:

> fatal: No names found, cannot describe anything.

I modified the Makefile and it now has a 4-digit commit name for me. That will be shorter for users to copy-paste while still accomodating a repository with thousands of commits.

If you want to continue using the 7-digit hashes, remove --abbrev=4 after merging.