Hey! I looked at the source code, but being new, could not figure out what was wrong. However, I found out that you could somehow use those XML files with "software lists" or something like that.
So I finally got the game running on Fedora Linux 27, but I do not really understand why.
I copied hash/sg1000.xml from the GIT source code tree to directory /usr/share/mame/hash
mv lode_runner_japan_europe.sg mpr-5998.ic1
mame sg1000 -window ldrun
starts the Lode Runner game using SG1000.