tk/extconf.rb: fix libpathflag arguments

* ext/tk/extconf.rb: fix to pass arrays instead of strings to
  libpathflag.  patch at [ruby-core:59665].  [Bug #9386]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44541 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-01-10

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44542 b2dd03c8-39d4-4d8f-98ff-823fe69b080e