you could indeed nuke /usr/src or, you could use
git status and / or git status --ignored to check tree changes, if you have them then git clean -nfdx to verify what to remove and git clean -fdx to finally remove offending changes but that culprit surely isn't in some options or in existing /usr/obj or in any (c)caches you might use? "nuclear option" on src tree gets quite a hassle after multiple tries but indeed does clean up everything really well while there, one can also copy and / or zfs snapshot a src tree, if git is a hassle to me git is first vcs ever that i really used as one, apart from a little svn. which i found easy to use but people vary
