path.h: add mkdir macro for mingw

mingw only supports the one-argument form of old windows.

fsnitroView.cpp: In function 'BOOL ViewFSNitroProc(HWND, UINT, WPARAM, LPARAM)':
fsnitroView.cpp:285:31: error: too many arguments to function 'int mkdir(const char*)'
         mkdir(tmp.c_str(),0777);
                               ^

desmume/src/path.h

@@ -27,6 +27,11 @@
 
 		#include "frontend/windows/winutil.h"
 		#include "frontend/windows/resource.h"
+
+#if defined(__MINGW32__)
+#define mkdir(A, B) mkdir(A)
+#endif
+
 #elif !defined(DESMUME_COCOA)
 	#include <glib.h>
 #endif /* HOST_WINDOWS */