Fix warning when doing Struct.new(:x, keyword_init: true){}

This is due to calling rb_mod_module_eval directly instead of using
rb_funcall_passing_block.

The problem with calling directly is it does not create a new VM
frame, so rb_mod_module_eval was called with no arguments, but with
the keyword given VM frame flag set, which causes problems
internally.

struct.c

@@ -569,7 +569,7 @@ rb_struct_s_def(int argc, VALUE *argv, VALUE klass)
     setup_struct(st, rest);
     rb_ivar_set(st, id_keyword_init, keyword_init);
     if (rb_block_given_p()) {
-	rb_mod_module_eval(0, 0, st);
+        rb_funcall_passing_block(st, rb_intern("module_eval"), 0, 0);
     }
 
     return st;

test/ruby/test_struct.rb

@@ -119,6 +119,16 @@ module TestStruct
     end
   end
 
+  def test_struct_new_with_keyword_init_and_block
+    struct = @Struct.new(:a, :b, keyword_init: true) do
+      def c
+        a + b
+      end
+    end
+
+    assert_equal(3, struct.new(a: 1, b: 2).c)
+  end
+
   def test_initialize
     klass = @Struct.new(:a)
     assert_raise(ArgumentError) { klass.new(1, 2) }