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From http://gcc.gnu.org/ml/gcc-patches/2009-11/msg00262.html

2009-10-30  Kai Tietz  <kai.tietz@onevision.com>

        * configure.ac: Disable target-winsup & co for
        x86_64-*-mingw* and *-w64-mingw* targets.
        * configure: Regenerated.