Fix build break on CentOS due to gcc 7.3.1

[codemzs]

Summary

Pursuant to discussion here https://reviews.llvm.org/D117113

[stella.stamenova]

LGTM

[labath]

I needed to dust off my old-deps build for another patch, so I also fixed this in the process.

[codemzs]

This comment was removed by codemzs.

[codemzs]

In D117637#3254195, @labath wrote:

I needed to dust off my old-deps build for another patch, so I also fixed this in the process.

@labath Have you already committed your change? I need this for our builds that are broken.

[labath]

It's in as 8bfa7a6dcc274bf46ce1587cf51996a3389ceb63.

lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp

       GetProcess().GetSignalInfo(GetID(), siginfo_buf->getBufferStart());
   if (!error.Success())
     return error.ToError();
-  return siginfo_buf;
+  return std::move(siginfo_buf);
 }