selfhost: port forrange — N_FORRANGE parser + cgen + tuple destructure

selfhost/cmd/wcc/check.ww

@@ -154,6 +154,32 @@ fn resolvewalk(c: *checker, n: *node) void = {
 		};
 	};
 
+	// `for (let x .. slice) body` / `for (let (a, b) .. slice) body` —
+	// each binding name becomes a fresh local. Walk the slice expr first
+	// so its idents resolve before the bindings shadow anything, then
+	// install bindings and walk the body/else.
+	if (k == nkind.N_FORRANGE) {
+		if (n.lhs != nil) { resolvewalk(c, n.lhs); };
+		if (n.list != nil) {
+			let m: *node = n.list;
+			for (m != nil) {
+				let bnm: str = m.str;
+				if (bnm.len > 0) {
+					scopedefine(c.cur, bnm, skind.SK_VAR, nil, m);
+				};
+				m = m.next;
+			};
+		} else {
+			let bnm: str = n.str;
+			if (bnm.len > 0) {
+				scopedefine(c.cur, bnm, skind.SK_VAR, nil, n);
+			};
+		};
+		if (n.body != nil) { resolvewalk(c, n.body); };
+		if (n.els  != nil) { resolvewalk(c, n.els);  };
+		return;
+	};
+
 	// `match (e) { case let v: T => stmt; ... }` — the binding `v`
 	// is declared by the case arm and visible inside its body.
 	if (k == nkind.N_MCASE) {