Only throw undefined instruction exception at execution, not at translation stage

Ryujinx/OsHle/Exceptions/UndefinedInstructionException.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace Ryujinx.OsHle.Exceptions
+{
+    public class UndefinedInstructionException : Exception
+    {
+        private const string ExMsg = "The instruction at 0x{0:x16} (opcode 0x{1:x8}) is undefined!";
+
+        public UndefinedInstructionException() : base() { }
+
+        public UndefinedInstructionException(long Position, int OpCode) : base(string.Format(ExMsg, Position, OpCode)) { }
+    }
+}