[LLDB] Fix RHEL 6 build and some Include What You Use warnings

[Eugene.Zelenko]

Summary

Build problem happens because of errno.

[labath]

thanks

lldb/trunk/source/Host/posix/MainLoopPosix.cpp

 //===-- MainLoopPosix.cpp ---------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "lldb/Host/posix/MainLoopPosix.h"
-
-#include <vector>
-
 #include "lldb/Core/Error.h"
+#include <algorithm>
+#include <cassert>
+#include <cerrno>
+#include <csignal>
+#include <vector>
+#include <sys/select.h>
 
 using namespace lldb;
 using namespace lldb_private;
 
 static sig_atomic_t g_signal_flags[NSIG];
 
 static void SignalHandler(int signo, siginfo_t *info, void *) {
   assert(signo < NSIG);