merge revision(s) 41648: [Backport #8115]

	* lib/mkmf.rb: should use expanded values for header directories
	  unless extmk.  patch by vo.x (Vit Ondruch) at [ruby-core:55653]
	  [Bug #8115], rhbz#921650.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@41658 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merge revision(s) 41254,41655: [Backport #8519]

	test_io.rb: fix test error

	* test/ruby/test_io.rb (TestIO#test_write_32bit_boundary): retry to
  remove the temporary file while EACCES occurs because of syncing in
  the system probably.  rescue ENOSPC from IO#tell.  [ruby-core:55457]
  [Bug #8519]
	* test/ruby/test_io.rb (TestIO#test_write_32bit_boundary): skip if
	  writing a file is slow.
	  [ruby-core:55541] [Bug #8519]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@41659 b2dd03c8-39d4-4d8f-98ff-823fe69b080e