ty: use `delay_span_bug` in `ty::AdtDef::eval_explicit_discr`.
ty: use `delay_span_bug` in `ty::AdtDef::eval_explicit_discr`.

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust