loader: Fix compilation on Windows with GCC
#define DLL_HANDLE HMODULE
#define DLL_OPEN(filename) LoadLibrary(filename)
#define DLL_CLOSE(handle) FreeLibrary(handle)
-#define DLL_GET_CREATE_FN(handle, name) (evmc_create_fn) GetProcAddress(handle, name)
+#define DLL_GET_CREATE_FN(handle, name) (evmc_create_fn)(uintptr_t) GetProcAddress(handle, name)
#define HAVE_STRCPY_S 1
#else
#include <dlfcn.h>
