[clang] [analyzer] Fix false double free when including 3rd-party headers with overloaded delete operator as system headers (PR #85224)

[Balazs Benics via cfe-commits]

steakhal wrote:

I had a deeper look at the patch and I think it's good.
To be on the safe side, I canonicalize `FD` to prefer decls with definitions if the redeclchain contains a definition.
This ensures that if we have a definition, `L` will refer to the beginning of that definition.

I'll merge this PR in a couple of days unless someone objects, or you challenge my proposed changes @Snape3058.
Thanks for the PR btw.

https://github.com/llvm/llvm-project/pull/85224