CMake: Find libusb include dir using pkg-config

Prior to this, only the library was discovered using pkg-config, while
the header was searched manually. This caused troubles on the CI when
building for OSX, as it would succeed to find the library but not the
header file.

Now, the manual search is now performed only when pkg-config cannot
locate a libusb package; which is what was already done for the library
file itself.

Signed-off-by: Paul Cercueil <[email protected]>

CMakeLists.txt

@@ -156,11 +156,12 @@ if (WITH_USB_BACKEND)
 		if (NOT LIBUSB_FOUND)
 			#Handle FreeBSD libusb and Linux libusb-1.0 libraries
 			find_library(LIBUSB_LIBRARIES NAMES usb-1.0 usb)
+			find_path(LIBUSB_INCLUDE_DIR libusb.h PATH_SUFFIXES libusb-1.0)
 		else()
 			set(LIBUSB_LIBRARIES ${LIBUSB_LINK_LIBRARIES})
+			set(LIBUSB_INCLUDE_DIR ${LIBUSB_INCLUDE_DIRS})
 		endif()
 	endif()
-	find_path(LIBUSB_INCLUDE_DIR libusb.h PATH_SUFFIXES libusb-1.0)
 	if (NOT LIBUSB_LIBRARIES OR NOT LIBUSB_INCLUDE_DIR)
 		message(SEND_ERROR "Unable to find libusb-1.0 dependency.\n"
 			"If you want to disable the USB backend, set WITH_USB_BACKEND=OFF.")