Tweaks of GCC 4.8.

* Remove obsolete ENV.m64. Configure will detect host triplets.
* Don't unset __GLIBCXX_DEBUG* as the original bug entry didn't actually
  suggest that.
* Make arch and osmajor standalone functions, and construct host triplet
  for build.
* Integrate '--enable-languages' into args.
* Make free functions into class.

Basically what applied to other GCC versions. Don't know why this one didn't get a pull request. Please review.