[AIX] Define __STDC_NO_ATOMICS__ and __STDC_NO_THREADS__ predefined macros

[Jake-Egan]

Summary

Transfer predefined macros, __STDC_NO_ATOMICS__ and __STDC_NO_THREADS__, from the AIX XL C/C++ compilers.

__STDC_NO_ATOMICS__ is needed because Open XL for AIX does not have C library atomics.

__STDC_NO_THREADS__ should be set until the OS implementation is complete because of conformance issues for AIX libc.

This patch replaces https://reviews.llvm.org/D103587.

[cebowleratibm]

Would like you to prune the new tests, then I think this will be ready to land.

clang/test/Preprocessor/init-ppc.c

726

Suggest pruning some of these. I don't think it's necessary to test every visible -std level.

[Jake-Egan]

Prune positive tests.

[Jake-Egan]

Add C17 test.

[Jake-Egan]

Fix formatting.

[cebowleratibm]

LGTM.

clang/lib/Basic/Targets/OSTargets.h

protected:
   void getOSDefines(const LangOptions &Opts, const llvm::Triple &Triple,
                     MacroBuilder &Builder) const override {
     DefineStd(Builder, "unix", Opts);
     Builder.defineMacro("_IBMR2");
     Builder.defineMacro("_POWER");
 
     Builder.defineMacro("_AIX");
 
+    if (LangStandard::getLangStandardForKind(Opts.LangStd).isC11()) {
+      Builder.defineMacro("__STDC_NO_ATOMICS__");
+      Builder.defineMacro("__STDC_NO_THREADS__");
+    }
+
     if (Opts.EnableAIXExtendedAltivecABI)
       Builder.defineMacro("__EXTABI__");
 
     unsigned Major, Minor, Micro;
     Triple.getOSVersion(Major, Minor, Micro);
 
     // Define AIX OS-Version Macros.
     // Includes logic for legacy versions of AIX; no specific intent to support.

clang/test/Preprocessor/init-ppc.c

 // PPC-AIX-NOWCHAR-NOT:#define _WCHAR_T 1
 
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char -pthread < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-THREADSAFE %s
 // PPC-AIX-THREADSAFE:#define _THREAD_SAFE 1
 
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-NOTHREADSAFE %s
 // PPC-AIX-NOTHREADSAFE-NOT:#define _THREAD_SAFE 1
 
+// RUN: %clang_cc1 -x c -std=c11 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-STDC %s
+// RUN: %clang_cc1 -x c -std=gnu11 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char  < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-STDC %s
+// PPC-AIX-STDC:#define __STDC_NO_ATOMICS__ 1
+// PPC-AIX-STDC:#define __STDC_NO_THREADS__ 1
+
+// RUN: %clang_cc1 -x c -std=c99 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX-STDC-N %s
+// PPC-AIX-STDC-N-NOT:#define __STDC_NO_ATOMICS__ 1
+// PPC-AIX-STDC-N-NOT:#define __STDC_NO_THREADS__ 1
+
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=powerpc-unknown-linux-gnu -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-LINUX %s
 //
 // PPC-LINUX:#define _ARCH_PPC 1
 // PPC-LINUX:#define _BIG_ENDIAN 1
 // PPC-LINUX-NOT:#define _LP64
 // PPC-LINUX:#define __BIGGEST_ALIGNMENT__ 16
 // PPC-LINUX:#define __BIG_ENDIAN__ 1
 // PPC-LINUX:#define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__