merge revision(s) 45488: [Backport #9631]

	* ext/readline/extconf.rb: fix typo, `$defs` not `$DEFS`.
	  [ruby-core:61756] [Bug #9578]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@45746 b2dd03c8-39d4-4d8f-98ff-823fe69b080e