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

[vsapsai]

Link to corresponding review that introduced the change is https://reviews.llvm.org/D45470

Another option is to use <atomic> and std::atomic but that will be functionality change. I'd rather avoid that.

[kubamracek]

[vsapsai]

Thanks for the quick review.

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

-// RUN: %clangxx_tsan %s -o %t -framework Foundation
+// RUN: %clangxx_tsan %s -o %t -framework Foundation -D__ALLOW_STDC_ATOMICS_IN_CXX__
 // RUN: %run %t 2>&1 | FileCheck %s
 
 #import <Foundation/Foundation.h>
 
 #import <memory>
 #import <stdatomic.h>
 
 _Atomic(long) destructor_counter = 0;

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

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

compiler-rt/test/tsan/Darwin/xpc-race.mm

-// RUN: %clangxx_tsan %s -o %t -framework Foundation
+// RUN: %clangxx_tsan %s -o %t -framework Foundation -D__ALLOW_STDC_ATOMICS_IN_CXX__
 // RUN: %deflake %run %t 2>&1 | FileCheck %s
 
 // UNSUPPORTED: ios
 
 #import <Foundation/Foundation.h>
 #import <xpc/xpc.h>
 #import <stdatomic.h>