patch cpp example to use passed CMAKE_CXX_STANDARD (#30835)
patch cpp example to use passed CMAKE_CXX_STANDARD (#30835)


grpc/grpc,stanley-cheung/grpc,stanley-cheung/grpc,jtattermusch/grpc,grpc/grpc,grpc/grpc,grpc/grpc,stanley-cheung/grpc,grpc/grpc,stanley-cheung/grpc,jtattermusch/grpc,stanley-cheung/grpc,stanley-cheung/grpc,stanley-cheung/grpc,jtattermusch/grpc,jtattermusch/grpc,grpc/grpc,stanley-cheung/grpc,jtattermusch/grpc,jtattermusch/grpc,stanley-cheung/grpc,jtattermusch/grpc,jtattermusch/grpc,grpc/grpc,jtattermusch/grpc,stanley-cheung/grpc,jtattermusch/grpc,grpc/grpc,grpc/grpc,grpc/grpc,jtattermusch/grpc,jtattermusch/grpc,stanley-cheung/grpc,grpc/grpc,grpc/grpc,stanley-cheung/grpc