Fix windows.h not found when cross compiling on Linux
The header provided by mingw-w64 on Linux is called windows.h.
#define WIN32_LEAN_AND_MEAN
#endif
-#include <Windows.h>
+#include <windows.h>
#if !defined(VK_USE_PLATFORM_WIN32_KHR)
#define VK_USE_PLATFORM_WIN32_KHR
#endif // #if !defined(VK_USE_PLATFORM_WIN32_KHR)
