symbol lookup error:pthread_create

想用树莓派做的事情：
树莓派利用视觉驱动小车找到目标物并执行相关操作；
目前情况：
1.树莓派安装的系统ubuntu mate16.04（系统还算稳定），系统中安装有opencv和wiringpi；
2.做的测试：go.c编写程序
#include <stdio.h>
#include <wiringPi.h>
#include <softPwm.h>
#include <errno.h>
#include <string.h>
#include <pthread.h>

#define foward_left   25
#define back_left     24
#define foward_right  21
#define back_right    22
#define pwm_left      23
#define pwm_right     14//电机
#define blower        0

int RANGE=100;
int vel_left,vel_right;

void setup()
{
  int ret=0;
  pinMode(foward_left,OUTPUT);
  pinMode(back_left,OUTPUT);  
  pinMode(foward_right,OUTPUT);
  pinMode(back_right,OUTPUT);
  ret=softPwmCreate (pwm_left, 0, RANGE);
  if(ret!=0)
  {
    printf（"error!\n");
  }
  ret=softPwmCreate (pwm_right, 0, RANGE);
  if(ret!=0)
  {
    printf（"error!\n");
  }
  pinMode(blower,OUTPUT);
}

void advance()
{
  digitalWrite(foward_left,HIGH);
  digitalWrite(back_left,LOW);
  digitalWrite(foward_right,HIGH);
  digitalWrite(back_right,LOW);
  softPwmWrite(pwm_left,vel_left);
  softPwmWrite(pwm_right,vel_right);
}
void turn()
{
  digitalWrite(foward_left,HIGH);
  digitalWrite(back_left,LOW);
  digitalWrite(foward_right,HIGH);
  digitalWrite(back_right,LOW);
  softPwmWrite(pwm_left,vel_left);
  softPwmWrite(pwm_right,vel_right);
}

void stop()
{
  digitalWrite(foward_left,LOW);
  digitalWrite(back_left,LOW);
  digitalWrite(foward_right,LOW);
  digitalWrite(back_right,LOW);
  softPwmWrite(pwm_left,vel_left);
  softPwmWrite(pwm_right,vel_right);
}

int main()
{
  int ret=0;
  if(wiringPiSetup()==-1)
  {
    ret=-1;
    printf( "wiringPi failed\n");
  }
  setup();
  vel_left=10;
  vel_right=10;
  advance();
  return 0;
}
gcc  go.c -o go -lwiringpi -pthread
编译，运行，没问题。

但若把程序名改成go.cpp（因为后期要用到opencv，需要写成c++程序）,编译成功，但运行./go时报错：symbol lookup error:pthread_create......

若用Cmakelists.txt编译，情况一样：
cmake_minimum_required(VERSION 2.8)
project(go C CXX)
SET(CMAKE_THREAD_PREFER_PTHREAD TRUE)
SET(CMAKE_C_FLAGS ${CMAKE_C_FLAGS} "-pthread")
set(CMAKE_LINKER_FLAGS "-pthread" CACHE STRING "Linker Flags" FORCE)
set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_LINKER_FLAGS}" CACHE STRING "" FORCE)
set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_LINKER_FLAGS}" CACHE STRING "" FORCE)
set(CMAKE_EXE_LINKER_FLAGS    "${CMAKE_LINKER_FLAGS}" CACHE STRING "" FORCE)
find_package(OpenCV REQUIRED)
find_package(Threads REQUIRED)
include_directories(${OpenCV_INCLUDE_DIRS} /home/liv/wiringPi-b0a60c3/devLib )
add_executable(go go.cpp)
target_link_libraries(go ${OpenCV_LIBS} wiringPi ${CMAKE_THREAD_LIBS_INIT})
#link_libraries(pthread)


求大神指教！！！