Properly reflect --with-opt-dir to LIBRUBY_DLDFLAGS on all platforms.

* configure.in (LIBRUBY_DLDFLAGS): Fix a bug where --with-opt-dir
  options given were not reflected to LIBRUBY_DLDFLAGS on many
  platforms including Linux and other GNU-based systems, NetBSD,
  AIX and BeOS.




git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39281 b2dd03c8-39d4-4d8f-98ff-823fe69b080e