Cannot compile eval group RegExp at runtime

```perl
$a = qr/(?{++$b})/;
$b = 7;
print qq[ok\n] if /$a$a/ && $b eq '9';
```

oneliner
```
> perlcc -r -e '$a = qr/(?{++$b})/; $b = 7; print qq[ok\n] if /$a$a/ && $b == 9;'
Eval-group not allowed at runtime, use re 'eval' in regex m/(?^:(?{++$b}))(?^:(?{++$b}))/ at -e line 1.
```

we are recompiling the RegExp at INIT time
