Interesting so this means that if someone really want llvm to support an extension (say a C attribute) that GCC supports, then you "just" have to make a contribution to the Linux kernel that use the gcc attribute and that is a minimum useful. Then LLVM will prioritize the support of said attribute.

As such, hardcore developers might become new Linux contributors just as an Indirect (but effective) way to force LLVM/clang to add support for an attribute.