configure.in: fix quoting brackets

* configure.in (RUBY_UNIVERSAL_ARCH): fix missing quoting
  brackets.  incorporated from
  http://www.opensource.apple.com/source/ruby/ruby-104/patches/configure.diff

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47823 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-10-07

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47824 b2dd03c8-39d4-4d8f-98ff-823fe69b080e