Enable dynamic linking against system libusb --with-system-libusb

configure.ac

@@ -333,16 +333,35 @@ AM_CONDITIONAL([HAVE_CURSES], [test x$curses = xyes])
 AM_CONDITIONAL([HAVE_WINDOWS], [test x$have_win32 = xtrue])
 AM_CONDITIONAL([HAVE_x86_64], [test x$have_x86_64 = xtrue])
 
-AC_CONFIG_SUBDIRS([compat/libusb-1.0])
 if test "x$want_usbutils" != xfalse; then
+	dlibusb="no"
 	AC_DEFINE([USE_USBUTILS], [1], [Defined to 1 if usbutils support required])
-	LIBUSB_LIBS="compat/libusb-1.0/libusb/.libs/libusb-1.0.a"
-	if test "x$have_linux" = "xtrue"; then
-		PKG_CHECK_MODULES([UDEV], [libudev], LIBUSB_LIBS+=" -ludev", [AC_MSG_ERROR([Missing required libudev dev])])
-	fi
-	if test "x$have_darwin" = "xtrue"; then
-		LIBUSB_LIBS+=" -lobjc"
-		LDFLAGS+=" -framework CoreFoundation -framework IOKit"
+	AC_ARG_WITH([system-libusb],
+		[AC_HELP_STRING([--with-system-libusb],[Compile against dynamic system libusb (default use included static libusb)])],
+		[dlibusb=$withval]
+	)
+
+	if test "x$dlibusb" != xno; then
+		case $target in
+			*-*-freebsd*)
+				LIBUSB_LIBS="-lusb"
+				LIBUSB_CFLAGS=""
+				AC_DEFINE(HAVE_LIBUSB, 1, [Define if you have libusb-1.0])
+				;;
+			*)
+				PKG_CHECK_MODULES(LIBUSB, libusb-1.0, [AC_DEFINE(HAVE_LIBUSB, 1, [Define if you have libusb-1.0])], [AC_MSG_ERROR([Could not find usb library - please install libusb-1.0])])
+				;;
+		esac
+	else
+		AC_CONFIG_SUBDIRS([compat/libusb-1.0])
+		LIBUSB_LIBS="compat/libusb-1.0/libusb/.libs/libusb-1.0.a"
+		if test "x$have_linux" = "xtrue"; then
+			LIBUSB_LIBS+=" -ludev"
+		fi
+		if test "x$have_darwin" = "xtrue"; then
+			LIBUSB_LIBS+=" -lobjc"
+			LDFLAGS+=" -framework CoreFoundation -framework IOKit"
+		fi
 	fi
 else
 	LIBUSB_LIBS=""