[clang] [llvm] [CodeGen][Clang] Add -fstack-protector-layout-only (PR #231651)

[via cfe-commits]

amosher-nvidia wrote:

Code was created with the assistance of Claude, but I reviewed and refined it all.

I submitted this as one PR because the Clang side is dependent on the LLVM side, but if needed/wanted I can split this up into two PRs, LLVM first, then Clang.

https://github.com/llvm/llvm-project/pull/231651