This fix is needed by PDFKit because it is a remapped framework[0],
the current code generates incorrect FieldAttribute on smart enums
because it uses `fa.LibraryName` as first option and this causes
remmaped frameworks have incorrect LibraryName generated for example
if a Field uses `+CoreImage` as `LibraryName` the following incorrect
code is generated:
```
[Field ("First", "+CoreImage")]
internal unsafe static IntPtr First {
get {
fixed (IntPtr *storage = &values [0])
return Dlfcn.CachePointer (Libraries.+CoreImage.Handle, "First", storage);
}
}
```
[0]: f5956d6cc1/src/generator.cs (L5985)
Alex Soto