fix: keep same ABI in asan and non-asan builds (#12831)

fixes: #12830

Closes #12831

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/12831 from jiulongw:jiulongw/fix 56f0ed68c1
PiperOrigin-RevId: 533192889

src/google/protobuf/parse_context.h

@@ -133,50 +133,41 @@ class PROTOBUF_EXPORT EpsCopyInputStream {
     if (count > 0) StreamBackUp(count);
   }
 
-#if defined(ABSL_HAVE_ADDRESS_SANITIZER) || defined(ABSL_HAVE_MEMORY_SANITIZER)
-  // In sanitizer mode we use an optional<int> to guarantee that:
+  // In sanitizer mode we use memory poisoning to guarantee that:
   //  - We do not read an uninitialized token.
   //  - Every non-empty token is moved from and consumed.
   class LimitToken {
    public:
-    LimitToken() = default;
-    explicit LimitToken(int token) : token_(token) {}
+    LimitToken() { PROTOBUF_POISON_MEMORY_REGION(&token_, sizeof(token_)); }
+    explicit LimitToken(int token) : token_(token) {
+      PROTOBUF_UNPOISON_MEMORY_REGION(&token_, sizeof(token_));
+    }
     LimitToken(LimitToken&& other) { *this = std::move(other); }
     LimitToken& operator=(LimitToken&& other) {
-      token_ = std::exchange(other.token_, absl::nullopt);
+      PROTOBUF_UNPOISON_MEMORY_REGION(&token_, sizeof(token_));
+      token_ = other.token_;
+      PROTOBUF_POISON_MEMORY_REGION(&other.token_, sizeof(token_));
       return *this;
     }
 
-    ~LimitToken() { ABSL_CHECK(!token_.has_value()); }
+    ~LimitToken() {
+#ifdef ADDRESS_SANITIZER
+      ABSL_CHECK(__asan_address_is_poisoned(&token_));
+#endif
+    }
 
     LimitToken(const LimitToken&) = delete;
     LimitToken& operator=(const LimitToken&) = delete;
 
     int token() && {
-      ABSL_CHECK(token_.has_value());
-      return *std::exchange(token_, absl::nullopt);
+      int t = token_;
+      PROTOBUF_POISON_MEMORY_REGION(&token_, sizeof(token_));
+      return t;
     }
 
-   private:
-    absl::optional<int> token_;
-  };
-#else
-  class LimitToken {
-   public:
-    LimitToken() = default;
-    explicit LimitToken(int token) : token_(token) {}
-    LimitToken(LimitToken&&) = default;
-    LimitToken& operator=(LimitToken&&) = default;
-
-    LimitToken(const LimitToken&) = delete;
-    LimitToken& operator=(const LimitToken&) = delete;
-
-    int token() const { return token_; }
-
    private:
     int token_;
   };
-#endif
 
   // If return value is negative it's an error
   PROTOBUF_NODISCARD LimitToken PushLimit(const char* ptr, int limit) {