cmake: detect libusb on FreeBSD

Source:
http://patch-tracker.debian.org/patch/series/view/rtl-sdr/0.5.0.4.4914-2/libusb-freebsd

Signed-off-by: Steve Markgraf <steve@steve-m.de>

cmake/Modules/FindLibUSB.cmake

@@ -8,7 +8,16 @@ if(NOT LIBUSB_FOUND)
     /usr/local/include
   )
 
-  find_library(LIBUSB_LIBRARIES NAMES usb-1.0
+#standard library name for libusb-1.0
+set(libusb1_library_names usb-1.0)
+
+#libusb-1.0 compatible library on freebsd
+if((CMAKE_SYSTEM_NAME STREQUAL "FreeBSD") OR (CMAKE_SYSTEM_NAME STREQUAL "kFreeBSD"))
+    list(APPEND libusb1_library_names usb)
+endif()
+
+  find_library(LIBUSB_LIBRARIES
+    NAMES ${libusb1_library_names}
     PATHS
     ${LIBUSB_PKG_LIBRARY_DIRS}
     /usr/lib