[Issue 19008] New: core.internal.convert.toUbyte doesn't work on enums

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19008

          Issue ID: 19008
           Summary: core.internal.convert.toUbyte doesn't work on enums
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: n8sh.secondary at hotmail.com

Problem demonstrated:

```
void main()
{
    import core.internal.convert : toUbyte;
    enum Month : uint { jan = 1}
    Month m = Month.jan;
    const bytes = toUbyte(m); // Doesn't compile.
}
```

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