Implement a more seamless way to provide missing functions on z/OS (#167703)

In this PR I'm changing the way we provide the missing functions like
strnlen() on z/OS from the separate header file to a wrapper around the
system headers that declare these functions. This will be less
intrusive.

---------

Co-authored-by: Zibi Sarbinowski <zibi@ca.ibm.com>

Author: perry-ca

clang/lib/AST/ByteCode/Context.cpp

@@ -21,7 +21,6 @@
 #include "clang/AST/ASTLambda.h"
 #include "clang/AST/Expr.h"
 #include "clang/Basic/TargetInfo.h"
-#include "llvm/Support/SystemZ/zOSSupport.h"
 
 using namespace clang;
 using namespace clang::interp;

llvm/CMakeLists.txt

@@ -1294,6 +1294,11 @@ if(LLVM_TARGET_IS_CROSSCOMPILE_HOST)
 # (this is a variable that CrossCompile sets on recursive invocations)
 endif()
 
+# Special hack for z/OS for missing POSIX functions
+if (CMAKE_SYSTEM_NAME MATCHES "OS390")
+  include_directories(SYSTEM "${LLVM_MAIN_INCLUDE_DIR}/llvm/Support/SystemZ/zos_wrappers" )
+endif()
+
 if( "${CMAKE_SYSTEM_NAME}" MATCHES SunOS )
    # special hack for Solaris to handle crazy system sys/regset.h
    include_directories("${LLVM_MAIN_INCLUDE_DIR}/llvm/Support/Solaris")

llvm/include/llvm/Support/SystemZ/zOSSupport.h

@@ -0,0 +1,35 @@
+//===- string.h - Common z/OS Include File ----------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares z/OS implementations for common functions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_ZOSWRAPPERS_STRING_H
+#define LLVM_SUPPORT_ZOSWRAPPERS_STRING_H
+
+#include_next <string.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// z/OS Unix System Services does not have support for:
+// - strsignal()
+// - strnlen()
+// Implementations are provided for z/OS.
+
+char *strsignal(int sig) asm("llvm_zos_strsignal");
+
+size_t strnlen(const char *S, size_t MaxLen) asm("llvm_zos_strnlen");
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

llvm/include/llvm/Support/SystemZ/zos_wrappers/string.h

@@ -10,7 +10,6 @@
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/SystemZ/zOSSupport.h"
 
 using namespace llvm;
 using namespace llvm::objcopy::macho;

llvm/lib/ObjCopy/MachO/MachOLayoutBuilder.cpp

@@ -8,7 +8,6 @@
 
 #include "MachOObject.h"
 #include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/Support/SystemZ/zOSSupport.h"
 
 using namespace llvm;
 using namespace llvm::objcopy::macho;

llvm/lib/ObjCopy/MachO/MachOObject.cpp

@@ -10,7 +10,6 @@
 #include "MachOObject.h"
 #include "llvm/BinaryFormat/MachO.h"
 #include "llvm/Object/MachO.h"
-#include "llvm/Support/SystemZ/zOSSupport.h"
 #include <memory>
 
 using namespace llvm;

llvm/lib/ObjCopy/MachO/MachOReader.cpp

@@ -19,7 +19,6 @@
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/LEB128.h"
-#include "llvm/Support/SystemZ/zOSSupport.h"
 #include "llvm/Support/WithColor.h"
 #include "llvm/Support/YAMLTraits.h"
 #include "llvm/Support/raw_ostream.h"

llvm/lib/ObjectYAML/MachOEmitter.cpp

@@ -15,7 +15,6 @@
 #include "llvm/BinaryFormat/MachO.h"
 #include "llvm/Support/YAMLTraits.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/Support/SystemZ/zOSSupport.h"
 #include "llvm/TargetParser/Host.h"
 #include <cstdint>
 #include <cstring>

llvm/lib/ObjectYAML/MachOYAML.cpp

@@ -311,6 +311,7 @@ add_llvm_component_library(LLVMSupport
   Threading.cpp
   Valgrind.cpp
   Watchdog.cpp
+  zOSLibFunctions.cpp
 
   ADDITIONAL_HEADER_DIRS
   Unix