isSame trait and literals

[Jack Applegame]

```d
enum isSame1(alias a, alias b) = __traits(isSame, a, b);
enum isSame2(args...)          = __traits(isSame, args[0], 
args[1]);

pragma(msg, isSame1!(1, 1)); //false
pragma(msg, isSame2!(1, 1)); //true

pragma(msg, isSame1!("test", "test")); //false
pragma(msg, isSame2!("test", "test")); //true
```
Looks like a bug.

try yourself: https://run.dlang.io/is/Edlz28