Enum.IsDefined does not work in reflection-free mode

[Thealexbarney]

Enum.IsDefined doesn't work in reflection-mode. This means that some APIs like Environment.GetFolderPath don't work.

A quick look in a debugger shows that the EnumInfo passed to GetEnumName has an empty Values array.

[MichalStrehovsky]

Enum APIs don't currently work: https://github.com/dotnet/corert/blob/master/Documentation/using-corert/reflection-free-mode.md#reflection-apis-that-are-up-for-discussion

I would like to fix that for the next incarnation of the reflection free mode that would make type metadata available, but still not allow reflection on fields and methods. It's likely such mode would be more practical. The current reflection-free mode (where nothing works) was just much cheaper to bring up.