Import ruby trunk r43725

> test_rdoc_generator_darkfish.rb: ignore nlink is not provided
>
> * test/rdoc/test_rdoc_generator_darkfish.rb (assert_hard_link): makes
>   no sense on platforms where link count is not provided.

Author: drbrain

test/test_rdoc_generator_darkfish.rb

@@ -214,7 +214,9 @@ def assert_hard_link filename
 
     begin
       FileUtils.ln src, dst
+      nlink = File.stat(dst).nlink if File.identical? src, dst
       FileUtils.rm dst
+      return if nlink == 1
     rescue SystemCallError
       return
     end