* ext/socket/extconf.rb (gai_strerror): checks if available and if
	  returns const pointer.
	* ext/socket/getaddrinfo.c (gai_strerror): defines only if non
	  available.  [ruby-core:21328]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8_7@22619 b2dd03c8-39d4-4d8f-98ff-823fe69b080e