Define MS_WINDOWS (and others) when compiling with MINGW

This is used throughout the Python code but is not defined
when compiling with Mingw-w64 compilers, so define it.

Co-authored-by: Алексей <alexey.pawlow@gmail.com>
Co-authored-by: Christoph Reiter <reiter.christoph@gmail.com>

Include/pyport.h

@@ -53,6 +53,21 @@
 #endif
 
 
+#ifdef __MINGW32__
+/* Translate GCC[mingw*] platform specific defines to those
+ * used in python code.
+ */
+#if !defined(MS_WIN64) && defined(_WIN64)
+#  define MS_WIN64
+#endif
+#if !defined(MS_WIN32) && defined(_WIN32)
+#  define MS_WIN32
+#endif
+#if !defined(MS_WINDOWS) && defined(MS_WIN32)
+#  define MS_WINDOWS
+#endif
+#endif /* __MINGW32__*/
+
 /**************************************************************************
 Symbols and macros to supply platform-independent interfaces to basic
 C language & library operations whose spellings vary across platforms.