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/tok.c

@@ -24,6 +24,7 @@ static const struct kwent kwtab[] = {
 	{ "def",      TK_DEF      },
 	{ "defer",    TK_DEFER    },
 	{ "else",     TK_ELSE     },
+	{ "enum",     TK_ENUM     },
 	{ "export",   TK_EXPORT   },
 	{ "false",    TK_FALSE    },
 	{ "fn",       TK_FN       },
@@ -99,6 +100,7 @@ tokname(Tkind k)
 	case TK_MATCH:		return "match";
 	case TK_CONST:		return "const";
 	case TK_UNDER:		return "_";
+	case TK_ENUM:		return "enum";
 
 	case TK_LPAREN:		return "(";
 	case TK_RPAREN:		return ")";