[MLIR][OpenMP][NFC] Use header guards for tblgen'd definitions#146684

Meinersbur merged 2 commits intollvm:mainllvm/llvm-project:mainfrom

Meinersbur:users/meinersbur/flang_canonical-loop_header-guardsMeinersbur/llvm-project:users/meinersbur/flang_canonical-loop_header-guardsCopy head branch name to clipboard