[TCP/Buffer] Add missing header

Differential Revision: D66674497

Pull Request resolved: #397

Author: Aidyn-A

gloo/transport/tcp/buffer.cc

@@ -9,6 +9,7 @@
 #include "gloo/transport/tcp/buffer.h"
 
 #include <string.h>
+#include <sys/syscall.h>
 #include <unistd.h>
 
 #include <iostream>
@@ -126,7 +127,7 @@ void Buffer::send(size_t offset, size_t length, size_t roffset) {
   GLOO_ENFORCE_LE(offset + length, size_);
 
   if (debug_) {
-    std::cout << "[" << getpid() << ": " << syscall(__NR_gettid) << "] ";
+    std::cout << "[" << getpid() << ": " << syscall(SYS_gettid) << "] ";
     std::cout << "send " << length << " bytes";
     std::cout << " to " << pair_->peer().str();
     std::cout << std::endl;