Update CMakeLists.txt

Former-commit-id: d239f45515a0c6f55facf2b33d33defe7cfcffe6

python/CMakeLists.txt

@@ -30,7 +30,7 @@ if (UNIX)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -fPIC")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fPIC")
   if (NOT ${U_CMAKE_BUILD_TYPE} MATCHES DEBUG)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility=hidden")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility=hidden -flto")
   endif()
 endif()