[clang] [llvm] [PAC][Driver] Implement `-mbranch-protection=pauthabi` option (PR #97237)

[Peter Smith via cfe-commits]

smithp35 wrote:

Apologies for the delay, I was out of office Thursday/Friday and wanted to discuss some possible options on the Monday call. I'll write something up based on the discussion tomorrow (Tuesday 9th) morning. I am at a conference for a lot of the week, so I maybe a bit slower to respond.

https://github.com/llvm/llvm-project/pull/97237