Adding use_system_libusb option for third_party/libusb

third_party/libusb/libusb/Makefile.am

Index: third_party/libusb/libusb/Makefile.am
diff --git a/third_party/libusb/libusb/Makefile.am b/third_party/libusb/libusb/Makefile.am
deleted file mode 100644
index 22661dccb7b7efa6589c43026a2dab4deb654c89..0000000000000000000000000000000000000000
--- a/third_party/libusb/libusb/Makefile.am
+++ /dev/null
@@ -1,40 +0,0 @@
-lib_LTLIBRARIES = libusb-1.0.la
-
-LINUX_USBFS_SRC = os/linux_usbfs.c
-DARWIN_USB_SRC = os/darwin_usb.c
-WINDOWS_USB_SRC = os/poll_windows.c os/windows_usb.c libusb-1.0.rc
-
-EXTRA_DIST = $(LINUX_USBFS_SRC) $(DARWIN_USB_SRC) $(WINDOWS_USB_SRC) \
-	os/threads_posix.c os/threads_windows.c
-
-if OS_LINUX
-OS_SRC = $(LINUX_USBFS_SRC)
-endif
-
-if OS_DARWIN
-OS_SRC = $(DARWIN_USB_SRC)
-AM_CFLAGS_EXT = -no-cpp-precomp
-endif
-
-if OS_WINDOWS
-OS_SRC = $(WINDOWS_USB_SRC)
-
-.rc.lo:
-	$(LIBTOOL) $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(RC) $(RCFLAGS) -i $< -o $@
-endif
-
-if THREADS_POSIX
-THREADS_SRC = os/threads_posix.h os/threads_posix.c
-else
-THREADS_SRC = os/threads_windows.h os/threads_windows.c
-endif
-
-libusb_1_0_la_CFLAGS = $(VISIBILITY_CFLAGS) $(AM_CFLAGS) $(THREAD_CFLAGS)
-libusb_1_0_la_LDFLAGS = $(LTLDFLAGS)
-libusb_1_0_la_SOURCES = libusbi.h core.c descriptor.c io.c sync.c $(OS_SRC) \
-	os/linux_usbfs.h os/darwin_usb.h os/windows_usb.h \
-	$(THREADS_SRC) \
-	os/poll_posix.h os/poll_windows.h
-
-hdrdir = $(includedir)/libusb-1.0
-hdr_HEADERS = libusb.h