Revert "[omp] drop parallel loop md (even if there is no clause)"

This reverts commit 84956a0.

Author: Simon Moll

clang/lib/CodeGen/CGStmtOpenMP.cpp

@@ -3330,9 +3330,6 @@ bool CodeGenFunction::EmitOMPWorksharingLoop(
               } else if (const auto *C = S.getSingleClause<OMPOrderClause>()) {
                 if (C->getKind() == OMPC_ORDER_concurrent)
                   CGF.LoopStack.setParallel(/*Enable=*/true);
-              } else {
-                // TODO: This may not be legal
-                CGF.LoopStack.setParallel(/*Enable=*/true);
               }
             },
             [IVSize, IVSigned, Ordered, IL, LB, UB, ST, StaticChunkedOne, Chunk,