We set these variables in the ebuild, so don't override them.

--- a/scripts/cmake.global
+++ b/scripts/cmake.global
@@ -27,16 +27,6 @@
 include_directories(AFTER ${LIBUSB_INCLUDE_PATH})
 set(CMAKE_REQUIRED_INCLUDES "${LIBUSB_INCLUDE_PATH};${CMAKE_REQUIRED_INCLUDES}")
 
-execute_process(COMMAND pkg-config --variable=systemdsystemunitdir systemd
-  OUTPUT_VARIABLE SYSTEMD_UNIT_DIR
-  ERROR_QUIET
-  OUTPUT_STRIP_TRAILING_WHITESPACE)
-
-execute_process(COMMAND pkg-config --variable=udevdir udev
-  OUTPUT_VARIABLE UDEV_DIR
-  ERROR_QUIET
-  OUTPUT_STRIP_TRAILING_WHITESPACE)
-
 macro(INSTALL_EXEC_CMD _COMMAND _FAILMSG)
 	install(CODE "
 		execute_process(COMMAND ${_COMMAND} RESULT_VARIABLE install_exec_res)