Fix cvar, ivar, const and method can be removed to frozen object

mrbgems/mruby-metaprog/src/metaprog.c

@@ -641,6 +641,7 @@ mrb_mod_remove_method(mrb_state *mrb, mrb_value mod)
   mrb_value *argv;
 
   mrb_get_args(mrb, "*", &argv, &argc);
+  mrb_check_frozen(mrb, mrb_obj_ptr(mod));
   while (argc--) {
     remove_method(mrb, mod, mrb_obj_to_sym(mrb, *argv));
     argv++;

mrbgems/mruby-metaprog/test/metaprog.rb

@@ -298,6 +298,9 @@ assert('Module#remove_class_variable', '15.2.2.4.39') do
   assert_raise(NameError) do
     Test4RemoveClassVariable.remove_class_variable(:@v)
   end
+  assert_raise(FrozenError) do
+    Test4RemoveClassVariable.freeze.remove_class_variable(:@@cv)
+  end
 end
 
 assert('Module#remove_method', '15.2.2.4.41') do
@@ -317,6 +320,7 @@ assert('Module#remove_method', '15.2.2.4.41') do
   assert_same klass, klass.class_eval{ remove_method :hello }
   assert_true klass.instance_methods.include? :hello
   assert_false klass.instance_methods(false).include? :hello
+  assert_raise(FrozenError) { klass.freeze.remove_method :m }
 end
 
 assert('Module.nesting', '15.2.2.2.2') do

src/variable.c

@@ -521,6 +521,7 @@ mrb_obj_iv_inspect(mrb_state *mrb, struct RObject *obj)
 MRB_API mrb_value
 mrb_iv_remove(mrb_state *mrb, mrb_value obj, mrb_sym sym)
 {
+  mrb_check_frozen(mrb, mrb_obj_ptr(obj));
   if (obj_iv_p(obj)) {
     iv_tbl *t = mrb_obj_ptr(obj)->iv;
     mrb_value val;

test/t/kernel.rb

@@ -404,6 +404,7 @@ assert('Kernel#remove_instance_variable', '15.3.1.3.41') do
   assert_equal nil, tri.var
   assert_raise(NameError) { tri.remove }
   assert_raise(NameError) { tri.remove_instance_variable(:var) }
+  assert_raise(FrozenError) { tri.freeze.remove }
 end
 
 # Kernel#require is defined in mruby-require. '15.3.1.3.42'

test/t/module.rb

@@ -262,6 +262,7 @@ assert('Module#remove_const', '15.2.2.4.40') do
   %i[x X!].each do |n|
     assert_raise(NameError) { Test4RemoveConst.remove_const(n) }
   end
+  assert_raise(FrozenError) { Test4RemoveConst.freeze.remove_const(:A) }
 end
 
 assert('Module#const_missing', '15.2.2.4.22') do