Transition frozen string to frozen root shape

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>

shape.c

@@ -203,14 +203,6 @@ rb_shape_transition_shape_frozen(VALUE obj)
     rb_shape_t* next_shape;
 
     if (shape == rb_shape_get_root_shape()) {
-        switch (BUILTIN_TYPE(obj)) {
-          case T_OBJECT:
-          case T_CLASS:
-          case T_MODULE:
-            break;
-          default:
-            return;
-        }
         next_shape = rb_shape_get_frozen_root_shape();
     }
     else {

spec/ruby/optional/capi/shared/rbasic.rb

@@ -10,7 +10,7 @@ describe :rbasic, shared: true do
     obj, _ = @data.call
     initial = @specs.get_flags(obj)
     obj.freeze
-    @specs.get_flags(obj).should == @freeze | initial
+    (@specs.get_flags(obj) & 0xFFFF).should == (@freeze | initial) & 0xFFFF
   end
 
   it "supports setting the FREEZE flag" do

test/ruby/test_string.rb

@@ -887,6 +887,18 @@ CODE
     end
   end
 
+  class StringWithIVSet < String
+    def set_iv
+      @foo = 1
+    end
+  end
+
+  def test_ivar_set_after_frozen_dup
+    str = StringWithIVSet.new.freeze
+    str.dup.set_iv
+    assert_raise(FrozenError) { str.set_iv }
+  end
+
   def test_each
     verbose, $VERBOSE = $VERBOSE, nil