Improve stability of Unity/Xamarin unit testing.

This commit avoids Mono's Regex StackOverflowException for non IL2CPP Unity
builds and non AOT Xamarin builds.

Author: yfakariya

test/MsgPack.UnitTest/MessagePackObjectTest.Miscs.cs

@@ -1,4 +1,4 @@
-#region -- License Terms --
+#region -- License Terms --
 //
 // MessagePack for CLI
 //
@@ -131,7 +131,7 @@ public void TestToString_ExtendedTypeObject_AsIs()
 		[Test]
 		public void TestToString_AllPossibleTypes_Success()
 		{
-#if MONO || XAMDROID
+#if MONO || ENABLE_MONO || ( XAMARIN && !AOT )
 			Assert.Inconclusive( "Mono Regex causes StackOverflow... ");
 #endif
 			TestToStringCore(