LLVM is not GPL'd because the FSF didn't want it.

GFK_of_xmaspast · on June 18, 2015

I got downvoted for this but: https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00...

fluidcruft · on June 18, 2015

Very interesting, I did not know that!

Maybe a better link (RMS's response when he recently discovers that Apple did indeed offer LLVM copyright assignment to FSF in 2005):

https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00...

Also note that 2005 is pre-GPLv3 and that Apple to this day dislikes GPLv3 so much that it continues to ship antiquated GPLv2 versions of GNU utilities in MacOS. So, my reading of the tea leaves is that the offer is not likely to be resurrected.