Fixed CMakeLists routing option (#874)

* If BAC_ROUTING was turned off, the gateway app wasn't deselected

CMakeLists.txt

@@ -865,12 +865,14 @@ if(BACNET_STACK_BUILD_APPS)
   add_executable(error apps/error/main.c)
   target_link_libraries(error PRIVATE ${PROJECT_NAME})
 
+  if(BAC_ROUTING)
     add_executable(gateway apps/gateway/main.c apps/gateway/gateway.h)
     target_link_libraries(gateway PRIVATE ${PROJECT_NAME})
     target_compile_options(gateway PRIVATE
       # Unreachable code because we have endless loop.
       $<$<C_COMPILER_ID:MSVC>:/wd4702>
     )
+  endif()
 
   add_executable(getevent apps/getevent/main.c)
   target_link_libraries(getevent PRIVATE ${PROJECT_NAME})