Enum that inherit UInt64 do not get right values

[bcardiff]

The compiler uses 32 bit integer to keep the values assigned to enum members.
If the Enum is declared with UInt64 as in https://github.com/crystal-lang/crystal/blob/master/src/llvm/enums.cr#L4 the user needs to assign values explicitly.

Affected lines https://github.com/crystal-lang/crystal/blob/master/src/compiler/crystal/semantic/top_level_visitor.cr#L683-L686

Extracted from #7262

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$ crystal --version
Crystal 0.27.0

[bcardiff]

@RX14 I think there is no need to fix this issue for 0.27.1, it has been there for a while already.