Make builtin binding fast again by binding only referenced symbols

Avoid doing the internal binding of top-level symbols in the parser,
leaving that work to be done in a post-processing step. For builtins,
this lets us do a reference-aware bind step (block_bind_incremental)
*after* generating builtins/0.

Libraries are a bit trickier since they may be bound multiple times, so
instead of thinking through the implications I added (block_bind_self)
to resolve all internal symbols immediately.

src/parser.y

@@ -331,7 +331,7 @@ FuncDefs:
   $$ = gen_noop();
 } |
 FuncDef FuncDefs {
-  $$ = block_bind($1, $2, OP_IS_CALL_PSEUDO);
+  $$ = block_join($1, $2);
 }
 
 Exp: