GNU contributed, but if they didn't exist Linux would either grow its own userspace or possibly borrow from *BSD. In the meantime, Linux did what GNU for some reason couldn't... although today HURD is actually nearly usable (in a VM) and Linux doesn't need GNU components (Alpine proves that musl/busybox can cover userspace, and with clang AFAIK you can make a completely GNU-free self-hosting system), which makes the whole thing a bit funnier to reason about.