[clang] Partially revert d8cd780.

The C11 atomics part was wrong.

(cherry picked from commit 95e6e1c)

Author: brad0

clang/lib/Basic/Targets/OSTargets.h

@@ -461,10 +461,8 @@ class LLVM_LIBRARY_VISIBILITY OpenBSDTargetInfo : public OSTargetInfo<Target> {
     if (this->HasFloat128)
       Builder.defineMacro("__FLOAT128__");
 
-    if (Opts.C11) {
-      Builder.defineMacro("__STDC_NO_ATOMICS__");
+    if (Opts.C11)
       Builder.defineMacro("__STDC_NO_THREADS__");
-    }
   }
 
 public:

clang/test/Preprocessor/init.c

@@ -1467,11 +1467,9 @@
 // RUN: %clang_cc1 -x c -std=c11 -E -dM -ffreestanding -triple=amd64-unknown-openbsd < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD-STDC %s
 // RUN: %clang_cc1 -x c -std=gnu11 -E -dM -ffreestanding -triple=amd64-unknown-openbsd < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD-STDC %s
 // RUN: %clang_cc1 -x c -std=c17 -E -dM -ffreestanding -triple=amd64-unknown-openbsd < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD-STDC %s
-// OPENBSD-STDC:#define __STDC_NO_ATOMICS__ 1
 // OPENBSD-STDC:#define __STDC_NO_THREADS__ 1
 //
 // RUN: %clang_cc1 -x c -std=c99 -E -dM -ffreestanding -triple=amd64-unknown-openbsd < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD-STDC-N %s
-// OPENBSD-STDC-N-NOT:#define __STDC_NO_ATOMICS__ 1
 // OPENBSD-STDC-N-NOT:#define __STDC_NO_THREADS__ 1
 //
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=xcore-none-none < /dev/null | FileCheck -match-full-lines -check-prefix XCORE %s