[clang] [PAC][clang][Driver] Add signed GOT flag (PR #96160)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Sorry, I made a mistake by approving #85235, which added a lot of driver options. It's not clear who are the initial ELF ptrauth users, but I am not sure with a very small user base, there are a lot of demands to customize the protection in such a fine-grained manner.

Using cc1 options looks fine.

https://github.com/llvm/llvm-project/pull/96160