[clang] [clang] Ensure pointers passed to runtime support functions are correctly signed (PR #98276)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

I notice the r+, but I haven't fully addressed this feedback - are you suggesting corrections in a follow up patch, or just conceptually approving with this PR? :D

https://github.com/llvm/llvm-project/pull/98276