[llvm] Add clang::lifetimebound annotation to ArrayRef constructors. (PR #113547)

[Gábor Horváth via llvm-commits]

================
@@ -113,7 +115,8 @@ namespace llvm {
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Winit-list-lifetime"
 #endif
-    constexpr /*implicit*/ ArrayRef(const std::initializer_list<T> &Vec)
+    constexpr /*implicit*/ ArrayRef(
+        const std::initializer_list<T> &Vec LLVM_LIFETIME_BOUND)
----------------
Xazax-hun wrote:

Hmm, actually, I am not sure if I'm super confident about this one.

Consider:
```
ArrayRef<int> ref({1, 2, 3, 4});
use(ref);
```

What would happen here? I wonder if this is actually safe despite the initializer list itself was a temporary and already destroyed when I invoke `use`. 

https://github.com/llvm/llvm-project/pull/113547