merge revision(s) 417b1a36447cb2c650de55b433ba623541fb8bb3: [Backport #19550]

	Fix memory leak for iclass

	[Bug #19550]

	If !RCLASS_EXT_EMBEDDED (e.g. 32 bit systems) then the rb_classext_t is
	allocated throug malloc so it must be freed.

	The issue can be seen in the following script:

	```
	20.times do
	  100_000.times do
	    mod = Module.new
	    Class.new do
	      include mod
	    end
	  end

	  # Output the Resident Set Size (memory usage, in KB) of the current Ruby process
	  puts `ps -o rss= -p #{$$}`
	end
	```

	Before this fix, the max RSS is 280MB, while after this change, it's
	30MB.
	---
	 gc.c                     |  2 +-
	 test/ruby/test_module.rb | 15 +++++++++++++++
	 2 files changed, 16 insertions(+), 1 deletion(-)

1 files changed, 15 insertions, 0 deletions

diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index 6c4defd6b1..54985f0f87 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -3274,6 +3274,21 @@ class TestModule < Test::Unit::TestCase
     assert_match(/::Foo$/, mod.name, '[Bug #14895]')
   end
 
+  def test_iclass_memory_leak
+    # [Bug #19550]
+    assert_no_memory_leak([], <<~PREP, <<~CODE, rss: true)
+      code = proc do
+        mod = Module.new
+        Class.new do
+          include mod
+        end
+      end
+      1_000.times(&code)
+    PREP
+      3_000_000.times(&code)
+    CODE
+  end
+
   private
 
   def assert_top_method_is_private(method)