Fix compile when not enable testing

* WITH_TESTING is a flag that user could configure

paddle/go/CMakeLists.txt

@@ -2,8 +2,10 @@ include_directories(${CMAKE_CURRENT_BINARY_DIR})
 
 go_library(adder SRCS adder.go)
 
-cc_test(cgo_test
+if (WITH_TESTING)
+  cc_test(cgo_test
         SRCS
         cgo_test.cc
         DEPS
         adder)
+endif()