ww: hare-feature batch (_, const, [_]T, ..., size/offset, assert, for-else)

cmd/wcc/ww.h

@@ -114,6 +114,8 @@ typedef enum {
 	TK_AS,		/* reserved for future cast spelling, not active */
 	TK_STATIC,	/* Hare-style storage-class qualifier */
 	TK_MATCH,	/* match expression head */
+	TK_CONST,	/* const binding */
+	TK_UNDER,	/* bare '_' discard */
 
 	/* punct + operators */
 	TK_LPAREN,	/* ( */
@@ -433,6 +435,7 @@ struct Sym {
 	Type		*type;
 	Node		*decl;
 	int		exported;
+	int		is_const;	/* const-bound (assignment rejected) */
 	Sym		*next;		/* iteration */
 	Sym		*hashnext;	/* bucket chain */
 	Scope		*scope;