Add a test for empty structs in HLSL hull shaders

Test/hlsl.emptystructreturn.tesc

@@ -0,0 +1,48 @@
+struct HullInputType
+{
+    float4 position : SV_Position;
+};
+
+struct ConstantOutputType
+{
+    float edges[3] : SV_TessFactor;
+    float inside : SV_InsideTessFactor;
+};
+struct EmptyStruct {};
+
+struct HullOutputType {};
+
+void blob(InputPatch<HullInputType, 3> patch)
+{
+}
+
+ConstantOutputType ColorPatchConstantFunction(InputPatch<HullInputType, 3> inputPatch, uint patchId : SV_PrimitiveID)
+{
+    ConstantOutputType output;
+
+	// Set the tessellation factors for the three edges of the triangle.
+    output.edges[0] = 2;
+    output.edges[1] = 2;
+    output.edges[2] = 2;
+
+	// Set the tessellation factor for tessallating inside the triangle.
+    output.inside = 2;
+
+    return output;
+}
+
+
+// Hull Shader
+[domain("tri")]
+[partitioning("integer")]
+[outputtopology("triangle_cw")]
+[outputcontrolpoints(3)]
+[patchconstantfunc("ColorPatchConstantFunction")]
+HullOutputType main(EmptyStruct stage_input, InputPatch<HullInputType, 3> patch, uint pointId : SV_OutputControlPointID, uint patchId : SV_PrimitiveID)
+{
+    HullOutputType output;
+    blob(patch);
+
+    return output;
+}
+