新手求助， error: template with C linkage

g++版本7.4.0

编译命令
g++ -c -std=c++11 -O3 -o myport myport.cpp -lrt -lpthread -Icore -Lcore

报错部分：

In file included from /usr/include/ctype.h:39:0,
                 from /usr/include/c++/7/cctype:42,
                 from /usr/include/c++/7/bits/localefwd.h:42,
                 from /usr/include/c++/7/string:43,
                 from core/***.h:26,
                 from core/***.h:4,
                 from myport.cpp:4:
core/***.h:29:1: error: template with C linkage
 template<bool ToLittle>
 ^~~~~~~~
In file included from core/***.h:30:0,
                 from core/***.h:4,
                 from myport.cpp:4:
/usr/include/netinet/tcp.h:102:17: error: redeclaration of ‘ uint8_t tcphdr::<unnamed union>::<unnamed struct>::th_off ’
  uint8_t th_off:4; /* data offset */
                 ^
/usr/include/netinet/tcp.h:99:17: note: previous declaration ‘ uint8_t tcphdr::<unnamed union>::<unnamed struct>::th_of ’
  uint8_t th_off:4; /* data offset */
                 ^
/usr/include/netinet/tcp.h:103:16: error: redeclaration of ‘ uint8_t tcphdr::<unnamed union>::<unnamed struct>::th_x2 ’
  uint8_t th_x2:4; /* (unused) */
                ^
/usr/include/netinet/tcp.h:98:16: note: previous declaration ‘ uint8_t tcphdr::<unnamed union>::<unnamed struct>::th_x2 ’
  uint8_t th_x2:4; /* (unused) */

由于强行转的 c/c++，很多基础不知道，来求助一下大佬们。迫于保密，部分已打码。

看描述有两个问题：

1. error: template with C linkage

搜了下，这个很多是 extern "C"导致的，我这边的是：

#ifdef __cplusplus
extern "C" {
#endif
#include "myport.h"
#ifdef __cplusplus
}
#endif

整段去掉都没用

2. 报错地点引用了以下头文件

#include <string>
#include <strings.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>       <-- 这行是 core/***.h:30:0
#include <arpa/inet.h>