[flang] Add scalar argument case for the Fortran Spread intrinsic unit test

[mleair]

Summary

The Fortran Spread intrinsic can take an array or a scalar source argument. The unit test had two tests but they both operated on arrays. This change adds a third Spread test where the source argument is a scalar.

[PeteSteinfeld]

All builds, tests, and looks good.

[mleair]

Close by commit: https://github.com/llvm/llvm-project/commit/d0f1ae6eb6eab82d2f67c61260087353a46d48ec

flang/unittests/RuntimeGTest/Transformational.cpp

TEST(Transformational, Spread) {
   EXPECT_EQ(result.GetDimension(0).LowerBound(), 1);
   EXPECT_EQ(result.GetDimension(0).Extent(), 3);
   EXPECT_EQ(result.GetDimension(1).LowerBound(), 1);
   EXPECT_EQ(result.GetDimension(1).Extent(), 2);
   for (int j{0}; j < 6; ++j) {
     EXPECT_EQ(*result.ZeroBasedIndexedElement<std::int32_t>(j), 1 + j % 3);
   }
   result.Destroy();
+
+  auto scalar{MakeArray<TypeCategory::Integer, 4>(
+      std::vector<int>{}, std::vector<std::int32_t>{1})};
+  RTNAME(Spread)(result, *scalar, 1, 2, __FILE__, __LINE__);
+  EXPECT_EQ(result.type(), array->type());
+  EXPECT_EQ(result.rank(), 1);
+  EXPECT_EQ(result.GetDimension(0).LowerBound(), 1);
+  EXPECT_EQ(result.GetDimension(0).Extent(), 2);
+  for (int j{0}; j < 2; ++j) {
+    EXPECT_EQ(*result.ZeroBasedIndexedElement<std::int32_t>(j), 1);
+  }
+  result.Destroy();
 }
 
 TEST(Transformational, Transpose) {
   // ARRAY  1 3 5
   //        2 4 6
   auto array{MakeArray<TypeCategory::Integer, 4>(
       std::vector<int>{2, 3}, std::vector<std::int32_t>{1, 2, 3, 4, 5, 6})};
   array->GetDimension(0).SetLowerBound(2); // shouldn't matter