[flang][OpenMP] Fix crash when arrays used in LINEAR clause (#175383) Closes #171007 Found this crash while testing OpenMP code - turns out putting an array in a LINEAR clause on SIMD directives causes the compiler to blow up with "unknown LLVM dialect type" and hit an UNREACHABLE. The issue is that LINEAR clauses only accept scalar variables (rank 0), but we weren't checking for that early enough. The invalid array type would slip through semantic analysis and then crash during MLIR to LLVM IR translation when it tried to convert the type. **What changed:** - Added a rank check in the LINEAR clause validation to catch arrays up front - Made an exception for `declare simd` with the REF modifier since that's actually allowed per spec - Added tests covering different array types (1D, multi-dim, assumed-shape) - Updated existing tests that now catch the new error Tested with the original reproducer and it now fails cleanly with a proper error message instead of crashing. GitOrigin-RevId: b76c84e70f4fb420b26b3887d9270fdb90d41933
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