[llvm] [polly] [IR] Don't allow successors() over block without terminators (PR #186646)

[Alexis Engelke via llvm-commits]

aengelke wrote:

MLIR OpenMP uses a different approach to create basic blocks and there can be more than one BB without a terminator.. the current approach of using analyses during IR construction makes this hardly fixable without deeper changes. IMO, analyses should be able to expect valid IR and not be used on IR-under-construction.

https://github.com/llvm/llvm-project/pull/186646