Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -70,6 +70,7 @@
 #include "llvm/Option/Option.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/ExitCodes.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/Host.h"
@@ -86,7 +87,6 @@
 #include <utility>
 #if LLVM_ON_UNIX
 #include <unistd.h> // getpid
-#include <sysexits.h> // EX_IOERR
 #endif
 
 using namespace clang::driver;
Index: llvm/cmake/config-ix.cmake
===================================================================
--- llvm/cmake/config-ix.cmake
+++ llvm/cmake/config-ix.cmake
@@ -53,6 +53,7 @@
 check_include_file(sys/stat.h HAVE_SYS_STAT_H)
 check_include_file(sys/time.h HAVE_SYS_TIME_H)
 check_include_file(sys/types.h HAVE_SYS_TYPES_H)
+check_include_file(sysexits.h HAVE_SYSEXITS_H)
 check_include_file(termios.h HAVE_TERMIOS_H)
 check_include_file(unistd.h HAVE_UNISTD_H)
 check_include_file(valgrind/valgrind.h HAVE_VALGRIND_VALGRIND_H)
Index: llvm/include/llvm/Support/ExitCodes.h
===================================================================
--- /dev/null
+++ llvm/include/llvm/Support/ExitCodes.h
@@ -0,0 +1,31 @@
+//===-- llvm/Support/ExitCodes.h - Exit codes for exit()  -------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file contains definitions of exit codes for exit() function. They are
+/// either defined by sysexits.h if it is supported, or defined here if
+/// sysexits.h is not supported.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_EXITCODES_H
+#define LLVM_SUPPORT_EXITCODES_H
+
+#if HAVE_SYSEXITS_H
+#include <sysexits.h>
+#elif __MVS__
+// <sysexits.h> does not exist on z/OS. The only value used in LLVM is
+// EX_IOERR, which is used to signal a special error condition (broken pipe).
+// Define the macro with its usual value from BSD systems, which is chosen to
+// not clash with more standard exit codes like 1.
+#define EX_IOERR 74
+#elif LLVM_ON_UNIX
+#error Exit code EX_IOERR not available
+#endif
+
+#endif
Index: llvm/lib/Support/CrashRecoveryContext.cpp
===================================================================
--- llvm/lib/Support/CrashRecoveryContext.cpp
+++ llvm/lib/Support/CrashRecoveryContext.cpp
@@ -9,14 +9,12 @@
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/ExitCodes.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/ThreadLocal.h"
 #include <mutex>
 #include <setjmp.h>
-#if LLVM_ON_UNIX
-#include <sysexits.h> // EX_IOERR
-#endif
 
 using namespace llvm;
 
Index: llvm/lib/Support/Unix/Signals.inc
===================================================================
--- llvm/lib/Support/Unix/Signals.inc
+++ llvm/lib/Support/Unix/Signals.inc
@@ -36,6 +36,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Config/config.h"
 #include "llvm/Demangle/Demangle.h"
+#include "llvm/Support/ExitCodes.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FileUtilities.h"
 #include "llvm/Support/Format.h"
@@ -46,7 +47,6 @@
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <string>
-#include <sysexits.h>
 #ifdef HAVE_BACKTRACE
 # include BACKTRACE_HEADER         // For backtrace().
 #endif