[lldb] Print empty enums as if they were unrecognised normal enums (#97553)

Fixes #97514

Given this example:
```
enum E {};

int main()
{
    E x = E(0);
    E y = E(1);
    E z = E(2);
    return 0;
}
```
lldb used to print nothing for `x`, but `0x1` for `y` and `0x2` for `z`.

At first this seemed like the 0 case needed fixing but the real issue
here is that en enum with no enumerators was being detected as a
"bitfield like enum".

Which is an enum where all enumerators are a single bit value, or the
sum of previous single bit values.

For these we do not print anything for a value of 0, as we assume it
must be the remainder after we've printed the other bits that were set
(I think this is also unfortunate, but I'm not addressing that here).

Clearly an enum with no enumerators cannot be being used as a bitfield,
so check that up front and print it as if it's a normal enum where we
didn't match any of the enumerators. This means you now get:
```
(lldb) p x
(E) 0
(lldb) p y
(E) 1
(lldb) p z
(E) 2
```

Which is a change to decimal from hex, but I think it's overall more
consistent. Printing hex here was never a concious decision.