wcc: Hare-style enum [storage] { ... } type

`type Foo = enum [intT] { NAME [= expr], ... };`. Storage defaults
to i32; members auto-increment from 0 (or last+1) when `= expr` is
omitted, and value expressions can reference earlier siblings —
enough surface for io::mode-style flag enums (`RDWR = READ | WRITE`).

`Foo.MEMBER` folds to an N_INTLIT in the checker, typed as the
named enum. Binops on enum values yield the same enum (type_eq on
the named pointer), so `mode.R | mode.W` is a `mode`. Enum ↔ int
is a reinterpret-only `as` cast — same register, no tag wrap — so
`mode.RDWR as i32` and `1 as mode` both work without runtime ops.

`is`/`?`/`!` are still tagged-union-only. CSP runtime (chan/proc)
is unchanged; only the type-system slot is touched here.

cmd/wcc/ast.c

@@ -86,6 +86,8 @@ nkname(Nkind k)
 	case N_VOIDLIT:		return "voidlit";
 	case N_TBANG:		return "tbang";
 	case N_YIELD:		return "yield";
+	case N_TENUM:		return "tenum";
+	case N_TENUMMEMBER:	return "tenummember";
 	case N_LAST:		return "last";
 	}
 	return "?";
@@ -158,6 +160,7 @@ pr(FILE *f, Node *n, int d)
 	case N_LET:
 	case N_TNAME:
 	case N_TFIELD:
+	case N_TENUMMEMBER:
 	case N_FIELD:
 	case N_ATTR:
 		if (n->str) { fputc(' ', f); printq(f, n->str); }