[clang] Thread Safety Analysis: Improved pointer handling (PR #127396)

[Marco Elver via cfe-commits]

melver wrote:

(Side-note: I cannot figure out what the canonical way to do "stacked commits" is for LLVM these days, so I'm just doing this the "old" way i.e. plain and simple normal git commits which I will commit separately after PR review.)

https://github.com/llvm/llvm-project/pull/127396