vm_invoke_builtin_delegate with start index.

opt_invokebuiltin_delegate and opt_invokebuiltin_delegate_leave
invokes builtin functions with same parameters of the method.
This technique eliminate stack push operations. However, delegation
parameters should be completely same as given parameters.
(e.g. `def foo(a, b, c) __builtin_foo(a, b, c)` is okay, but
__builtin_foo(b, c) is not allowed)

This patch relaxes this restriction. ISeq has a local variables
table which includes parameters. For example, the method defined
as `def foo(a, b, c) x=y=nil`, then local variables table contains
[a, b, c, x, y]. If calling builtin-function with arguments which
are sub-array of the lvar table, use opt_invokebuiltin_delegate
instruction with start index. For example, `__builtin_foo(b, c)`,
`__builtin_bar(c, x, y)` is okay, and so on.

mini_builtin.c

@@ -21,6 +21,11 @@ rb_load_with_builtin_functions(const char *feature_name, const struct rb_builtin
 
     rb_ast_dispose(ast);
 
+    // for debug
+    if (0 && strcmp("prelude", feature_name) == 0) {
+        rb_io_write(rb_stdout, rb_iseq_disasm((const rb_iseq_t *)iseq));
+    }
+
     // register (loaded iseq will not be freed)
     st_insert(loaded_builtin_table, (st_data_t)feature_name, (st_data_t)iseq);
     rb_gc_register_mark_object((VALUE)iseq);