[llvm] [IR] Add CallBr intrinsics support (PR #133907)

[Robert Imschweiler via llvm-commits]

ro-i wrote:

@Meinersbur you added `polly/test/ScopDetect/callbr.ll` a few years ago. As far as I understand, this currently conflicts with my interpretation of how callbr should be handled during region detection (see failing test). I think that the region of the callbr instruction should include every following block that does not postdominate the block that has callbr as its terminator.
Or, simpler said, a region is only a region if the exit block postdominates every preceding callbr - that's what I implemented in `llvm/include/llvm/Analysis/RegionInfoImpl.h`.
How do you think about that?

https://github.com/llvm/llvm-project/pull/133907