LZ4: vendoring in the kernel

Patches that fix security problems in the context of the kernel but aren't appropriate in userspace sound extremely fragile: what happens when the upstream project adds another function that the kernel would have to change?

Seems like it would be worthwhile for the upstream project to have a header file with all of the bits of functions a user like the kernel might need to change, and the kernel could compile with a kernel-specific header file instead.