.git/exclude
--assume-unchanged
--no-update-index
And fwiw, I think global/home-dir .gitignore is bad, for everything except of OS-level spam like .DS-Store
I have dependency_tree globally excluded because it is my unique naming convention. Actually it might just be my unique approach because other people don't seem to mind having 1000 overrides for libraries they don't use.
My preference of not having much in my global gitignore is only sensible for my particular daily work, if you need to partially track build folders in projects and can't control the ignore files automatically, a global ignore might make sense.