Compiling libcxx with gcc 4.6.4 (MingW) produces these errors:

 type_traits:3280:31: error: expected primary-expression before 'decltype'
 type_traits:3280:29: error: expected ';' at end of member declaration

 memory:2415:49: error: function 'std::__1::default_delete<_Tp>::default_delete()'
 defaulted on its first declaration must not have an exception-specification

 memory:2435:49: error: function 'std::__1::default_delete<_Tp []>::default_delete()'
 defaulted on its first declaration must not have an exception-specification

The attached patch defines _LIBCPP_HAS_NO_ADVANCED_SFINAE and
_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS for gcc version < 4.7, making
the library compile with gcc 4.6.4.