[clang] [clang][CFG] Change child order in Reverse Post Order (RPO) iteration. (PR #80030)

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

I agree that this is a change other clients would also benefit from. I am not that worried about breaking other users, RPO is a partial ordering, and now we are picking a different (but valid) order. Clients depending on this detail are depending on an implementation detail and it would probably be Hyrum's law in action. I do not have an example where the old behavior would be desirable, so I think it might be better to change/fix the clients in that case. If we are proven wrong, we can always introduce a non-type template argument as a customization point to revert to the old behavior.  

https://github.com/llvm/llvm-project/pull/80030