[clang] [Clang] Add `noalias` to `this` pointer in C++ constructors (PR #136792)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

These days, there's very high demand for "secure" C/C++.  From this perspective, this optimization is a security threat: if you write code that does an undefined write to "this", you have a lurking security vulnerability could be exposed with any change to optimization heuristics.

People who care about this kind of thing want strong sanitizers, and flags to define as much undefined behavior as possible.

https://github.com/llvm/llvm-project/pull/136792