[SystemZ][z/OS] Add AutoConvert.h header to MemoryBuffer.cpp

[abhina.sreeskantharajan]

Summary

This commit https://github.com/llvm/llvm-project/commit/75e164f61d391979b4829bf2746a5d74b94e95f2 removed the AutoConvert.h header causing a build break on z/OS. This patch adds it back to fix it.

[zibi]

LGTM

llvm/lib/Support/MemoryBuffer.cpp

 //===--- MemoryBuffer.cpp - Memory Buffer implementation ------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 //  This file implements the MemoryBuffer interface.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Config/config.h"
+#include "llvm/Support/AutoConvert.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/SmallVectorMemoryBuffer.h"