Fixed also argument forwarding in class_exec

Pointed out by @matz.
https://github.com/mruby/mruby/pull/6391#issuecomment-2433662139

mrbgems/mruby-class-ext/src/class.c

@@ -4,6 +4,7 @@
 #include <mruby/array.h>
 #include <mruby/proc.h>
 #include <mruby/variable.h>
+#include <mruby/internal.h>
 #include <mruby/presym.h>
 
 static mrb_value
@@ -44,18 +45,7 @@ mod_singleton_class_p(mrb_state *mrb, mrb_value self)
 static mrb_value
 mod_module_exec(mrb_state *mrb, mrb_value self)
 {
-  const mrb_value *argv;
-  mrb_int argc;
-  mrb_value blk;
-
-  mrb_get_args(mrb, "*&!", &argv, &argc, &blk);
-
-  struct RClass *c = mrb_class_ptr(self);
-  if (mrb->c->ci->cci > 0) {
-    return mrb_yield_with_class(mrb, blk, argc, argv, self, c);
-  }
-  mrb_vm_ci_target_class_set(mrb->c->ci, c);
-  return mrb_yield_cont(mrb, blk, self, argc, argv);
+  return mrb_object_exec(mrb, self, mrb_class_ptr(self));
 }
 
 struct subclass_args {

mrbgems/mruby-class-ext/test/class.rb

@@ -27,3 +27,20 @@ assert 'Class#attached_object' do
   assert_raise(TypeError){TrueClass.attached_object}
   assert_raise(TypeError){NilClass.attached_object}
 end
+
+assert 'Class#class_exec' do
+  c = Class.new
+  class << c
+    def index
+      12345
+    end
+  end
+  c.class_exec do
+    def index
+      54321
+    end
+  end
+
+  assert_equal 12345, c.index
+  assert_equal 54321, c.new.index
+end