[llvm] [ADT] Add `[[clang::lifetimebound]]` annotations to Twine.h (PR #210474)

[via llvm-commits]

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@@ -424,7 +431,8 @@ class Twine {
   /// @name String Operations
   /// @{
 
-  Twine concat(const Twine &Suffix) const;
+  Twine
+  concat(const Twine &Suffix LLVM_LIFETIME_BOUND) const LLVM_LIFETIME_BOUND;
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isuckatcs wrote:

> The only benefit I see in marking definition is that you won't have to look at the declaration to figure out that a parameter is lifetime bound.

This. I only want it for readability purposes.

https://github.com/llvm/llvm-project/pull/210474