[Cython] Small patch for __stdcall

The following small patch gets rid of some warnings on the cygwin
platform (it it not WIN32 but does have definitions of __stdcall
resulting in warnings).

Please let me know if it will or won't get into the upstream release.

Thanks.

Cython/Compiler/ModuleNode.py

@@ -274,8 +274,10 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
         code.putln("#if PY_VERSION_HEX < 0x02040000")
         code.putln("  #define METH_COEXIST 0")
         code.putln("#endif")
-        code.putln("#ifndef WIN32")
+        code.putln("#ifndef __stdcall")
         code.putln("  #define __stdcall")
+        code.putln("#endif")
+        code.putln("#ifndef __cdecl")
         code.putln("  #define __cdecl")
         code.putln("#endif")
         self.generate_extern_c_macro_definition(code)