- Only build interpreter with version >= 4.11, not 4.09. The latter
  doesn't work because of some BCO# trouble. This shouldn't make a
  real difference to (sane) compiler people, who always do at least
  a two-stage bootstrap.

- Nuke some -K2m options when building with GHC >= 4.11, because it's
  not understood (yet) and doesn't seem to be necessary anymore.