undefined symbol: USER_ERROR__missing_dlib_all_source_cpp_file__OR__inconsistent_use_of_DEBUG_or_ENA

解决办法如下：

1、先找到threads文件夹下的threads_kernel_shared.h；

2、将下面这段代码注释掉就可以了：

//#ifdef ENABLE_ASSERTS  
//    extern int USER_ERROR__missing_dlib_all_source_cpp_file__OR__inconsistent_use_of_DEBUG_or_ENABLE_ASSERTS_preprocessor_directives;  
//    inline int dlib_check_consistent_assert_usage() { USER_ERROR__missing_dlib_all_source_cpp_file__OR__inconsistent_use_of_DEBUG_or_ENABLE_ASSERTS_preprocessor_directives = 0; return 0; }  
//#else  
//    extern int USER_ERROR__missing_dlib_all_source_cpp_file__OR__inconsistent_use_of_DEBUG_or_ENABLE_ASSERTS_preprocessor_directives_;  
//    inline int dlib_check_consistent_assert_usage() { USER_ERROR__missing_dlib_all_source_cpp_file__OR__inconsistent_use_of_DEBUG_or_ENABLE_ASSERTS_preprocessor_directives_ = 0; return 0; }  
//#endif  
//    const int dlib_check_assert_helper_variable = dlib_check_consistent_assert_usage();