Check for cyclic prepend before making origin

It's important to only make the origin when the prepend goes
through, as the precense of the origin informs whether to do an
origin backfill.

This plus 2d877327e fix [Bug #17590].

test/ruby/test_module.rb

@@ -485,6 +485,19 @@ class TestModule < Test::Unit::TestCase
     assert_equal([m], m.ancestors)
   end
 
+  def test_bug17590
+    m = Module.new
+    c = Class.new
+    c.prepend(m)
+    c.include(m)
+    m.prepend(m) rescue nil
+    m2 = Module.new
+    m2.prepend(m)
+    c.include(m2)
+
+    assert_equal([m, c, m2] + Object.ancestors, c.ancestors)
+  end
+
   def test_prepend_works_with_duped_classes
     m = Module.new
     a = Class.new do