Compilation error with tdm-mingw (4.7.1) in case of enabled c++11 (Bugfix #2555)

If you try to compile something with enabled c++11 support it will fail with a linker error:
undefined reference: __sync_fetch_and_add

The root of the problem is the definition of CV_XADD in Core/operations.hpp:67:

    #if !defined WIN32 && (defined __i486__ || defined __i586__ || \
        defined __i686__ || defined __MMX__ || defined __SSE__  || defined __ppc__)
      #define CV_XADD __sync_fetch_and_add
    #else
      #include <ext/atomicity.h>
      #define CV_XADD __gnu_cxx::__exchange_and_add
    #endif

At the first line it checks whether it's on Windows or not (i.e. MINGW or not), but it checks only WIN32 but not _WIN32.
According to the MSDN the "standard" is _WIN32, and it looks like the WIN32 is not defined in C++0x mode in TDM-MINGW

I think the safe solution would be to change the first line to something like this:

    #if !(defined WIN32 OR defined _WIN32) && (defined __i486__ || defined __i586__ || \