[Bug c/80378] Extend alloc_size attribute for better Linux kernel checking

[andi-gcc at firstfloor dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80378

--- Comment #1 from Andi Kleen <andi-gcc at firstfloor dot org> ---
Small correction: argument 4 would need to be a constant for shifted by.