windows/README: Deprecate mingw32, suggest using mingw64.

pfalcon · pfalcon · commit aeadf7607d36 · 2015-11-01T01:05:33.000+03:00
Ubuntu's mingw32 has gcc 4.2.1, which is rather old and has incorrect
non-initialized variable analysis which produces warnings, which
per MicroPython default settings get turned into errors.
diff --git a/windows/README b/windows/README
@@ -6,6 +6,13 @@ consider to contribute.
 
 To cross-compile under Debian/Ubuntu Linux system:
 
+sudo apt-get install gcc-mingw-w64
+make CROSS_COMPILE=i686-w64-mingw32-
+
+If for some reason mingw64 crosscompiler is not available, you can try
+mingw32 instead, but it come with really old gcc which may produce some
+spurious errors (you may need to disable -Werror):
+
 sudo apt-get install mingw32 mingw32-binutils mingw32-runtime
 make CROSS_COMPILE=i586-mingw32msvc-
 
