FIX: explicit linking against std++ breaks under mingw32.

I'm not sure this won't trigger other failures, but used to be like
this and worked fine ...

scikits/learn/setup.py

@@ -42,7 +42,6 @@ def configuration(parent_package='', top_path=None):
                          sources=[join('src', 'ball_tree.cpp')],
                          depends=[join('src', 'BallTree.h'),
                                   join('src', 'BallTreePoint.h')],
-                         libraries=["stdc++"],
                          include_dirs=[numpy.get_include()])
 
     # the following packages depend on cblas, so they have to be build