[SystemZ][z/OS] Set short-enums as the default for z/OS

[Jonathan.Crowther]

Summary

This patch sets short-enums to be the default for z/OS.

[SeanP]

clang/test/Driver/zos-driver-defaults.c

2

Can you add an additional test for -fno-short-enum to make sure that works too.

[zibi]

LGTM, though not sure why comment is referencing -fshort-enums=0.
If '=0' is not significant perhaps delete it to remove confusion.

[Jonathan.Crowther]

Added a test for -fno-short-enums

[abhina.sreeskantharajan]

LGTM

[Jonathan.Crowther]

Forgot to set the repository for my last patch. No code changes.

clang/lib/Driver/ToolChains/Clang.cpp

if (Args.hasFlag(options::OPT_fno_elide_constructors,
     CmdArgs.push_back("-fno-elide-constructors");
 
   ToolChain::RTTIMode RTTIMode = TC.getRTTIMode();
 
   if (KernelOrKext || (types::isCXX(InputType) &&
                        (RTTIMode == ToolChain::RM_Disabled)))
     CmdArgs.push_back("-fno-rtti");
 
-  // -fshort-enums=0 is default for all architectures except Hexagon.
+  // -fshort-enums=0 is default for all architectures except Hexagon and z/OS.
   if (Args.hasFlag(options::OPT_fshort_enums, options::OPT_fno_short_enums,
-                   TC.getArch() == llvm::Triple::hexagon))
+                   TC.getArch() == llvm::Triple::hexagon || Triple.isOSzOS()))
     CmdArgs.push_back("-fshort-enums");
 
   RenderCharacterOptions(Args, AuxTriple ? *AuxTriple : RawTriple, CmdArgs);
 
   // -fuse-cxa-atexit is default.
   if (!Args.hasFlag(
           options::OPT_fuse_cxa_atexit, options::OPT_fno_use_cxa_atexit,
           !RawTriple.isOSAIX() && !RawTriple.isOSWindows() &&

clang/test/Driver/zos-driver-defaults.c

+// RUN: %clang -### --target=s390x-none-zos -fsyntax-only %s 2>&1 | FileCheck --check-prefix=CHECK-SHORT-ENUMS %s
+// RUN: %clang -### --target=s390x-none-zos -fno-short-enums -fsyntax-only %s 2>&1 | FileCheck %s
+// REQUIRES: clang-driver
+
+//CHECK-SHORT-ENUMS: -fshort-enums
+//CHECK-SHORT-ENUMS: -fno-signed-char
+
+//CHECK-NOT: -fshort-enums
+//CHECK: -fno-signed-char