fix macro redefinition warnings on win-glfw build

src/audio/sampman_miles.cpp

@@ -1,3 +1,4 @@
+#define WITHWINDOWS
 #include "common.h"
 
 #ifdef AUDIO_MSS

src/control/Script.cpp

@@ -2209,8 +2209,9 @@ int scriptToLoad = 0;
 const char *scriptfile = "main.scm";
 
 #ifdef _WIN32
-#include <Windows.h>
+extern "C" __declspec(dllimport) short __stdcall GetAsyncKeyState(int);
 #endif
+
 int open_script()
 {
 	// glfwGetKey doesn't work because of CGame::Initialise is blocking