Hojun-Cho
3252bd1709
A computed enum member — B = A + 4, RW = R | W, sibling/chained backref — left its value-expr node nil-typed: enumvalfold folds the constant but never stamps the expr, and since enum members are not installed as scope idents the sibling backref resolves to nothing, so BOTH the N_BIN/N_UN wrapper and the backref N_IDENT go nil (literal members are fine). Stamp the value-expr subtree (only-nil) to the enum's underlying storage type via a new stampenumvals/stampnilexpr pass on the N_TENUM branch. Mirrors harec checking each member value-expr at the underlying type (ref/harec/src/check.c:4419). A prerequisite for arming the wwstage asserttyped bail. Checker-only — the value folds to a constant at every use site and in cgen, so the node's type_ is never read by codegen; 990-997 byte-id hold. Extends the 901 gap-corpus with 901_enum_corpus.ww.