[clang] [clang][OpenMP] Diagnose badly-formed collapsed imperfect loop nests (#60678) (PR #101305)

[Julian Brown via cfe-commits]

jtb20 wrote:

OpenMPIterationSpaceChecker is still passed a pointer to CollapsedLoopDecls, because one caller passes a nullptr, and we don't want to do the analysis in that case.

https://github.com/llvm/llvm-project/pull/101305