[MLIR][OpenMP] NFC: Update parallel workshare loop reduction tests (#105835)

This patch updates MLIR tests for `omp.parallel` + `omp.wsloop`
reductions to move the reduction clause into `omp.wsloop` rather than
the parent `omp.parallel`, as mandated by the spec for these cases and
also to match what Flang is already producing for `parallel do
reduction(...)` combined constructs.

From the OpenMP Spec version 5.2, section 17.2:

> The effect of the reduction clause is as if it is applied to all leaf
constructs that permit the clause, except for the following constructs:
> - The `parallel` construct, when combined with the `sections`,
worksharing-loop, `loop`, or `taskloop` construct; [...]

Author: skatrak

mlir/test/Dialect/OpenMP/ops.mlir

@@ -1019,10 +1019,10 @@ func.func @parallel_reduction_byref() {
 func.func @parallel_wsloop_reduction(%lb : index, %ub : index, %step : index) {
   %c1 = arith.constant 1 : i32
   %0 = llvm.alloca %c1 x i32 : (i32) -> !llvm.ptr
-  // CHECK: omp.parallel reduction(@add_f32 %{{.*}} -> %{{.+}} : !llvm.ptr) {
-  omp.parallel reduction(@add_f32 %0 -> %prv : !llvm.ptr) {
-    // CHECK: omp.wsloop {
-    omp.wsloop {
+  // CHECK: omp.parallel {
+  omp.parallel {
+    // CHECK: omp.wsloop reduction(@add_f32 %{{.*}} -> %{{.+}} : !llvm.ptr) {
+    omp.wsloop reduction(@add_f32 %0 -> %prv : !llvm.ptr) {
       // CHECK: omp.loop_nest (%{{.+}}) : index = (%{{.+}}) to (%{{.+}}) step (%{{.+}}) {
       omp.loop_nest (%iv) : index = (%lb) to (%ub) step (%step) {
         %1 = arith.constant 2.0 : f32
@@ -1216,10 +1216,10 @@ func.func @parallel_reduction2() {
 func.func @parallel_wsloop_reduction2(%lb : index, %ub : index, %step : index) {
   %c1 = arith.constant 1 : i32
   %0 = llvm.alloca %c1 x i32 : (i32) -> !llvm.ptr
-  // CHECK: omp.parallel reduction(@add2_f32 %{{.*}} -> %{{.+}} : !llvm.ptr) {
-  omp.parallel reduction(@add2_f32 %0 -> %prv : !llvm.ptr) {
-    // CHECK: omp.wsloop {
-    omp.wsloop {
+  // CHECK: omp.parallel {
+  omp.parallel {
+    // CHECK: omp.wsloop reduction(@add2_f32 %{{.*}} -> %{{.+}} : !llvm.ptr) {
+    omp.wsloop reduction(@add2_f32 %0 -> %prv : !llvm.ptr) {
       // CHECK: omp.loop_nest (%{{.+}}) : index = (%{{.+}}) to (%{{.+}}) step (%{{.+}}) {
       omp.loop_nest (%iv) : index = (%lb) to (%ub) step (%step) {
         %1 = arith.constant 2.0 : f32

mlir/test/Target/LLVMIR/openmp-reduction.mlir

@@ -540,8 +540,8 @@ llvm.func @parallel_nested_workshare_reduction(%ub : i64) {
   %lb = llvm.mlir.constant(1 : i64) : i64
   %step = llvm.mlir.constant(1 : i64) : i64
 
-  omp.parallel reduction(@add_i32 %0 -> %prv : !llvm.ptr) {
-    omp.wsloop {
+  omp.parallel {
+    omp.wsloop reduction(@add_i32 %0 -> %prv : !llvm.ptr) {
       omp.loop_nest (%iv) : i64 = (%lb) to (%ub) step (%step) {
         %ival = llvm.trunc %iv : i64 to i32
         %lprv = llvm.load %prv : !llvm.ptr -> i32