[clang] [Clang] Mark this pointer in destructors dead_on_return (PR #166276)

[John McCall via cfe-commits]

rjmccall wrote:

You're correct to be conservative about virtual bases, because they will generally still be live out of the base subobject destructor. I think it's worth doing this for non-virtual bases just to avoid needing an excessive number of controlling flags, since otherwise I assume people might want a staging flag that disables this just for classes with bases.

https://github.com/llvm/llvm-project/pull/166276