Auto merge of #1429 - RalfJung:discriminant_value, r=RalfJung
Auto merge of #1429 - RalfJung:discriminant_value, r=RalfJung

test discriminant_value intrinsic

Make sure this works for all types, not just enums/generators.

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri