Only generate code for those builtin functions actually used.

Makes output of --debug-dump-disasm much simpler.

compile.h

@@ -50,6 +50,7 @@ void block_append(block* b, block b2);
 block block_join(block a, block b);
 int block_has_only_binders(block, int bindflags);
 block block_bind(block binder, block body, int bindflags);
+block block_bind_referenced(block binder, block body, int bindflags);
 
 int block_compile(block, struct locfile*, struct bytecode**);