phobos's circle CI runs a busted version of DMD

[deadalnix]

Sample code:
```d
     ushort ee = 1028;
     ee <<= 5U;
     ee >>= 5U;
     writeln(ee);
```

Regular compiler: https://godbolt.org/z/TcbjP76fW (prints 1028)
Circle CI: 64516 .

Someone, the compiler manages to do a signed arithmetic shift on 
an unsigned.