[clang] Introduce intra-procedural lifetime analysis in Clang (PR #142313)

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

> implement a warning (maybe return-stack-addr) in this patch.

This patch is already big enough. But I think a small comment of how reporting will work down the line might be useful. 

https://github.com/llvm/llvm-project/pull/142313