[TSan] Avoid triggering assert when program calls OSAtomicCompareAndSwapLong

[yln]

Summary

A previous change brought the new, relaxed implementation of "on failure
memory ordering" for synchronization primitives in LLVM over to TSan
land [1]. It included the following assert:

// 31.7.2.18: "The failure argument shall not be memory_order_release
// nor memory_order_acq_rel". LLVM (2021-05) fallbacks to Monotonic
// (mo_relaxed) when those are used.
CHECK(IsLoadOrder(fmo));

static bool IsLoadOrder(morder mo) {
  return mo == mo_relaxed || mo == mo_consume
      || mo == mo_acquire || mo == mo_seq_cst;
}

A previous workaround for a false positive when using an old Darwin
synchronization API assumed this failure mode to be unused and passed a
dummy value [2]. We update this value to mo_relaxed which is also the
value used by the actual implementation to avoid triggering the assert.

[1] https://reviews.llvm.org/D99434
[2] https://reviews.llvm.org/D21733

rdar://78122243

compiler-rt/lib/tsan/rtl/tsan_interceptors_mac.cpp

 
 namespace __tsan {
 
 // The non-barrier versions of OSAtomic* functions are semantically mo_relaxed,
 // but the two variants (e.g. OSAtomicAdd32 and OSAtomicAdd32Barrier) are
 // actually aliases of each other, and we cannot have different interceptors for
 // them, because they're actually the same function.  Thus, we have to stay
 // conservative and treat the non-barrier versions as mo_acq_rel.
-static const morder kMacOrderBarrier = mo_acq_rel;
-static const morder kMacOrderNonBarrier = mo_acq_rel;
+static constexpr morder kMacOrderBarrier = mo_acq_rel;
+static constexpr morder kMacOrderNonBarrier = mo_acq_rel;
+static constexpr morder kMacFailureOrder = mo_relaxed;
 
 #define OSATOMIC_INTERCEPTOR(return_t, t, tsan_t, f, tsan_atomic_f, mo) \
   TSAN_INTERCEPTOR(return_t, f, t x, volatile t *ptr) {                 \
     SCOPED_TSAN_INTERCEPTOR(f, x, ptr);                                 \
     return tsan_atomic_f((volatile tsan_t *)ptr, x, mo);                \
   }
 
 #define OSATOMIC_INTERCEPTOR_PLUS_X(return_t, t, tsan_t, f, tsan_atomic_f, mo) \

 OSATOMIC_INTERCEPTORS_BITWISE(OSAtomicXor, fetch_xor,
                               OSATOMIC_INTERCEPTOR_PLUS_X, OSATOMIC_INTERCEPTOR)
 
 #define OSATOMIC_INTERCEPTORS_CAS(f, tsan_atomic_f, tsan_t, t)              \
   TSAN_INTERCEPTOR(bool, f, t old_value, t new_value, t volatile *ptr) {    \
     SCOPED_TSAN_INTERCEPTOR(f, old_value, new_value, ptr);                  \
     return tsan_atomic_f##_compare_exchange_strong(                         \
         (volatile tsan_t *)ptr, (tsan_t *)&old_value, (tsan_t)new_value,    \
-        kMacOrderNonBarrier, kMacOrderNonBarrier);                          \
+        kMacOrderNonBarrier, kMacFailureOrder);                             \
   }                                                                         \
                                                                             \
   TSAN_INTERCEPTOR(bool, f##Barrier, t old_value, t new_value,              \
                    t volatile *ptr) {                                       \
     SCOPED_TSAN_INTERCEPTOR(f##Barrier, old_value, new_value, ptr);         \
     return tsan_atomic_f##_compare_exchange_strong(                         \
         (volatile tsan_t *)ptr, (tsan_t *)&old_value, (tsan_t)new_value,    \
-        kMacOrderBarrier, kMacOrderNonBarrier);                             \
+        kMacOrderBarrier, kMacFailureOrder);                                \
   }
 
 OSATOMIC_INTERCEPTORS_CAS(OSAtomicCompareAndSwapInt, __tsan_atomic32, a32, int)
 OSATOMIC_INTERCEPTORS_CAS(OSAtomicCompareAndSwapLong, __tsan_atomic64, a64,
                           long_t)
 OSATOMIC_INTERCEPTORS_CAS(OSAtomicCompareAndSwapPtr, __tsan_atomic64, a64,
                           void *)
 OSATOMIC_INTERCEPTORS_CAS(OSAtomicCompareAndSwap32, __tsan_atomic32, a32,