Got constrained callvirt working.

Tests/SimpleStructsAndArraysTest/ConstrainedTest.cs

@@ -0,0 +1,72 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Cosmos.TestRunner;
+
+namespace SimpleStructsAndArraysTest
+{
+    public interface ITestMutate
+    {
+        void Mutate();
+    }
+
+    public struct MyStruct1 : ITestMutate
+    {
+        public int a;
+
+        public void Mutate()
+        {
+            a++;
+        }
+    }
+
+    public struct MyStruct2
+    {
+        public int b;
+
+        public override string ToString()
+        {
+            b++;
+            return b.ToString();
+        }
+    }
+
+    internal struct MyStruct3
+    {
+        public int c;
+
+        public override string ToString()
+        {
+            c = 1;
+            return c.ToString();
+        }
+    }
+
+    public static class ConstrainedTest
+    {
+        public static void DoMutate<T>(ref T a) where T : ITestMutate
+        {
+            a.Mutate();
+        }
+
+        public static void MutateStructTest()
+        {
+            var xS1 = new MyStruct1();
+            Assert.IsTrue(xS1.a == 0, "xS1.a == 0");
+            DoMutate(ref xS1);
+            Assert.IsTrue(xS1.a == 1, "xS1.a == 1");
+
+            var xS2 = new MyStruct2();
+            Assert.IsTrue(xS2.b == 0, "xS2.b == 0");
+            Assert.IsTrue(xS2.ToString() == "1", "xS2.ToString() == '1'");
+            Assert.IsTrue(xS2.b == 1, "xS2.b == 1");
+
+            var xS3 = new MyStruct3();
+            Assert.IsTrue(xS3.c == 0, "xS3.b == 0");
+            Assert.IsTrue(xS3.ToString() == "1", "xS3.ToString() == '1'");
+            Assert.IsTrue(xS3.c == 1, "xS3.b == 1");
+        }
+    }
+}