[compiler-rt] [asan] Add experimental 'track_poison' flag (PR #133175)

[Vitaly Buka via llvm-commits]

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@@ -119,7 +181,7 @@ void __asan_poison_memory_region(void const volatile *addr, uptr size) {
       if (beg.offset > 0) {
         *beg.chunk = Min(value, beg.offset);
       } else {
-        *beg.chunk = kAsanUserPoisonedMemoryMagic;
+        *beg.chunk = poison_magic;
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vitalybuka wrote:

1. we should have no "race conditions", though it helps with contention, but I'd prefer simpler version, which does not redefine shadow constants
2. It's on report only, perf is not important.

https://github.com/llvm/llvm-project/pull/133175