CMake: do not compile tests if NO_TEST is specified

CMakeLists.txt

@@ -31,6 +31,6 @@ set(PARSERS header dns dhcp http igmp ssdp coap)
 
 # Subdirectories containing code
 add_subdirectory(src)
-IF( NOT OPENWRT_CROSSCOMPILING )
+IF( NOT (NO_TEST OR OPENWRT_CROSSCOMPILING) )
     add_subdirectory(test)
 ENDIF()