libusb: require pkg-config support

An alternative approach to show how much cleaner the pure pkg-config
way is.

This changes the discovery procedures for libusb-1.0 and libusb-0.1,
making them depend on pkg-config being properly installed and
configured, including the necessary build host configuration for the
cross-builds (see
http://www.flameeyes.eu/autotools-mythbuster/pkgconfig/cross-compiling.html)

It should make it possible to compile OpenOCD without changes and
extra effort on GNU/Linux, FreeBSD users would need to supply a .pc
file for their libusb implementation or add LIBUSB1_LIBS and
LIBUSB1_CFLAGS to the configure environment.

Change-Id: I826e378dd1e0d101a549a573b2c63212a7e00b64
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1467
Reviewed-by: Xiaofan <xiaofanc@gmail.com>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Tested-by: Spencer Oliver <spen@spen-soft.co.uk>

src/jtag/drivers/Makefile.am

@@ -6,6 +6,8 @@ libocdjtagdrivers_la_LIBADD =
 libocdjtagdrivers_la_SOURCES = \
 	$(DRIVERFILES)
 
+libocdjtagdrivers_la_CPPFLAGS = $(AM_CPPFLAGS) $(LIBUSB1_CFLAGS) $(LIBUSB0_CFLAGS)
+
 ULINK_FIRMWARE = $(srcdir)/OpenULINK
 
 EXTRA_DIST = $(ULINK_FIRMWARE)

src/jtag/drivers/libusb1_common.h

@@ -22,7 +22,7 @@
 #ifndef JTAG_LIBUSB_COMMON_H
 #define JTAG_LIBUSB_COMMON_H
 
-#include <libusb-1.0/libusb.h>
+#include <libusb.h>
 
 #define jtag_libusb_device			libusb_device
 #define jtag_libusb_device_handle		libusb_device_handle

src/jtag/drivers/mpsse.c

@@ -24,7 +24,7 @@
 
 #include "mpsse.h"
 #include "helper/log.h"
-#include <libusb-1.0/libusb.h>
+#include <libusb.h>
 
 /* Compatibility define for older libusb-1.0 */
 #ifndef LIBUSB_CALL

src/jtag/drivers/ti_icdi_usb.c

@@ -33,7 +33,7 @@
 
 #include <target/cortex_m.h>
 
-#include <libusb-1.0/libusb.h>
+#include <libusb.h>
 
 #define ICDI_WRITE_ENDPOINT 0x02
 #define ICDI_READ_ENDPOINT 0x83