Externals: Update libusb to 1.0.23-rc1

Now has support for isochronous transfers in the WinUSB backend,
which may or may not work better than the UsbDk backend.

Externals/libusb/Xcode/config.h

@@ -0,0 +1,25 @@
+/* config.h.  Manually generated for Xcode.  */
+
+/* Default visibility */
+#define DEFAULT_VISIBILITY /**/
+
+/* Message logging */
+#define ENABLE_LOGGING 1
+
+/* Define to 1 if you have the <poll.h> header file. */
+#define HAVE_POLL_H 1
+
+/* Define to 1 if you have the <sys/time.h> header file. */
+#define HAVE_SYS_TIME_H 1
+
+/* Darwin backend */
+#define OS_DARWIN 1
+
+/* type of second poll() argument */
+#define POLL_NFDS_TYPE nfds_t
+
+/* Use POSIX Threads */
+#define THREADS_POSIX 1
+
+/* Use GNU extensions */
+#define _GNU_SOURCE 1