Func eval of functions that take 16-byte input structs corrupts the input

[gregg-miskelly]

Build a debuggee with the following code:

    public class Program
    {
        public static DateTime ReturnInput(DateTime input)
        {
            return input; 
        }

        public static void Main(string[] args)
        {
            DateTime now = DateTime.Now;
            Console.WriteLine(now); // set breakpoint here
        }
    }

1. Set a breakpoint on the call to Console.WriteLine
2. In the debugger evaluate now and ReturnInput(now)

Result:
The two variables have different values:

now
{09/08/2016 12:34:49}
ReturnInput(now)
{06/24/0001 02:59:04}

Expected:
Two values should be the same

[mikem8361]

PR dotnet/coreclr#7149 fix this.