libusb: Fix build issues under cygwin/mingw

This fixes issues with the folliwing patch under cygwin/mingw builds.
http://openocd.zylin.com/236

Change-Id: I7dd0b2d09cc64568bc99b16aa32e791a8273c5db
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/240
Tested-by: jenkins
Reviewed-by: Mathias Küster <kesmtp@freenet.de>
Reviewed-by: Mauro Gamba <maurillo71@gmail.com>

src/jtag/drivers/libusb0_common.h

@@ -36,7 +36,7 @@
 #define jtag_libusb_reset_device(dev)		usb_reset(dev)
 #define jtag_libusb_get_device(devh)		usb_device(devh)
 
-inline int jtag_libusb_claim_interface(jtag_libusb_device_handle *devh,
+static inline int jtag_libusb_claim_interface(jtag_libusb_device_handle *devh,
 				       int iface)
 {
 	return usb_claim_interface(devh, iface);

src/jtag/drivers/libusb1_common.h

@@ -36,7 +36,7 @@
 #define jtag_libusb_reset_device(dev)		libusb_reset_device(dev)
 #define jtag_libusb_get_device(devh)		libusb_get_device(devh)
 
-inline int jtag_libusb_claim_interface(jtag_libusb_device_handle *devh,
+static inline int jtag_libusb_claim_interface(jtag_libusb_device_handle *devh,
 				       int iface)
 {
 	return libusb_claim_interface(devh, iface);