message: add_custom_command rather than add_custom_target
  Avoid patching in every build
diff: @@ -308,7 +308,7 @@ function(sign_app_library name app_oe_conf_path enclave_sign_key_path)
  -e ${CMAKE_CURRENT_BINARY_DIR}/lib${name}.so
  -c ${app_oe_conf_path}
  -k ${enclave_sign_key_path}
  - DEPENDS ${name}
  + DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/lib${name}.so
  ${app_oe_conf_path}
  ${enclave_sign_key_path}
  )
  @@ -344,9 +344,11 @@ endif()
  function(create_patched_enclave_lib name app_oe_conf_path enclave_sign_key_path)
  set(patched_name ${name}.patched)
  - add_custom_target(${patched_name}
  - COMMAND cp ${CMAKE_CURRENT_BINARY_DIR}/lib${name}.so ${CMAKE_CURRENT_BINARY_DIR}/lib${patched_name}.so
  - COMMAND PYTHONPATH=${CCF_DIR}/tests:$ENV{PYTHONPATH} python3 patch_binary.py -p ${CMAKE_CURRENT_BINARY_DIR}/lib${patched_name}.so
  + set(patched_lib_name lib${patched_name}.so)
  + add_custom_command(
  + OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${patched_lib_name}
  + COMMAND cp ${CMAKE_CURRENT_BINARY_DIR}/lib${name}.so ${CMAKE_CURRENT_BINARY_DIR}/${patched_lib_name}
  + COMMAND PYTHONPATH=${CCF_DIR}/tests:$ENV{PYTHONPATH} python3 patch_binary.py -p ${CMAKE_CURRENT_BINARY_DIR}/${patched_lib_name}
  WORKING_DIRECTORY ${CCF_DIR}/tests
  DEPENDS ${name}
  )
  