[ASan][ADT] Don't scribble with ASan

AddressSanitizer (ASAN) disables scribbling to prevent overwriting poisoned objects.
Needed by llvm#79049

Author: Advenam Tacet

llvm/include/llvm/ADT/FunctionExtras.h

@@ -317,8 +317,10 @@ template <typename ReturnT, typename... ParamTs> class UniqueFunctionBase {
     // Clear the old callback and inline flag to get back to as-if-null.
     RHS.CallbackAndInlineFlag = {};
 
-#ifndef NDEBUG
-    // In debug builds, we also scribble across the rest of the storage.
+#if !defined(NDEBUG) && !(defined(ADDRESS_SANITIZER) || defined(__SANITIZE_ADDRESS__))
+    // In debug builds without ASan, we also scribble across the rest of the storage.
+    // AddressSanitizer (ASAN) disables scribbling to prevent overwriting poisoned objects
+    // (e.g., annotated short strings).
     memset(RHS.getInlineStorage(), 0xAD, InlineStorageSize);
 #endif
   }