Add cmake module for finding udev.

This adds a cmake module to find udev/libudev for linux.

cmake/Modules/FindLibUDev.cmake

+# Once done these will be defined:
+#
+#  UDEV_FOUND
+#  UDEV_INCLUDE_DIRS
+#  UDEV_LIBRARIES
+
+find_package(PkgConfig QUIET)
+if (PKG_CONFIG_FOUND)
+	pkg_check_modules(_UDEV QUIET udev)
+endif()
+
+find_path(UDEV_INCLUDE_DIR
+	NAMES libudev.h
+	HINTS
+		${_UDEV_INCLUDE_DIRS}
+	PATHS
+		/usr/include /usr/local/include /opt/local/include)
+
+find_library(UDEV_LIB
+	NAMES udev libudev
+	HINTS
+		${_UDEV_LIBRARY_DIRS}
+	PATHS
+		/usr/lib /usr/local/lib /opt/local/lib)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(UDev DEFAULT_MSG UDEV_LIB UDEV_INCLUDE_DIR)
+mark_as_advanced(UDEV_INCLUDE_DIR UDEV_LIB)
+
+if(UDEV_FOUND)
+	set(UDEV_INCLUDE_DIRS ${UDEV_INCLUDE_DIR})
+	set(UDEV_LIBRARIES ${UDEV_LIB})
+endif()