[clang] [Clang] Disable use of the counted_by attribute for whole struct pointers (PR #112636)

[Jan Hendrik Farr via cfe-commits]

Cydox wrote:

> It's probably worthwhile to perform some analysis to see if using that to calculate the new size results in allocation size changes in the kernel. If not, then perhaps we could reinstate the "whole struct" code.

This can calculation can result in both larger and smaller sizes compared to what the kernel currently does, so we can't reinstate the whole struct code until the `struct_size` macro in the kernel is changed if we want clang to use this calculation.

https://github.com/llvm/llvm-project/pull/112636