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.

test/wcc/700_e2e.c

@@ -1086,6 +1086,20 @@ static const struct row rows[] = {
 	  "  let e: str = r as str;\n"
 	  "  return e.len: i32;\n"
 	  "};", 3 },
+	/* enum: auto-increment, explicit value, sibling-ref */
+	{ "type color = enum { RED, GREEN, BLUE };\n"
+	  "fn main() i32 = { return color.BLUE as i32; };", 2 },
+	{ "type mode = enum u8 { R = 1, W = 2, RW = R | W };\n"
+	  "fn main() i32 = {\n"
+	  "  let m: mode = mode.RW;\n"
+	  "  return m as i32;\n"
+	  "};", 3 },
+	/* enum: bitwise op between two members yields the same enum type */
+	{ "type mode = enum u8 { R = 1, W = 2 };\n"
+	  "fn main() i32 = {\n"
+	  "  let m: mode = mode.R | mode.W;\n"
+	  "  return m as i32;\n"
+	  "};", 3 },
 	{ NULL, 0 }
 };