Revert "Follow-up to r331378. Update tests to allow to use C atomics in C++."

It reverts commit r331484 because it caused test failures

    ThreadSanitizer-x86_64 :: Darwin/gcd-groups-destructor.mm
    ThreadSanitizer-x86_64 :: Darwin/libcxx-shared-ptr-stress.mm
    ThreadSanitizer-x86_64 :: Darwin/xpc-race.mm

Foundation.h transitively includes <atomic>, so we have a case of benign mixing
<stdatomic.h> and <atomic>.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@331491 91177308-0d34-0410-b5e6-96231b3b80d8

Author: vsapsai

test/tsan/Darwin/gcd-groups-destructor.mm

@@ -1,4 +1,4 @@
-// RUN: %clangxx_tsan %s -o %t -framework Foundation -D__ALLOW_STDC_ATOMICS_IN_CXX__
+// RUN: %clangxx_tsan %s -o %t -framework Foundation
 // RUN: %run %t 2>&1 | FileCheck %s
 
 #import <Foundation/Foundation.h>

test/tsan/Darwin/libcxx-shared-ptr-stress.mm

@@ -1,4 +1,4 @@
-// RUN: %clangxx_tsan %s -o %t -framework Foundation -D__ALLOW_STDC_ATOMICS_IN_CXX__
+// RUN: %clangxx_tsan %s -o %t -framework Foundation
 // RUN: %run %t 2>&1 | FileCheck %s
 
 #import <Foundation/Foundation.h>

test/tsan/Darwin/xpc-race.mm

@@ -1,4 +1,4 @@
-// RUN: %clangxx_tsan %s -o %t -framework Foundation -D__ALLOW_STDC_ATOMICS_IN_CXX__
+// RUN: %clangxx_tsan %s -o %t -framework Foundation
 // RUN: %deflake %run %t 2>&1 | FileCheck %s
 
 // UNSUPPORTED: ios