[llvm] [llvm] Add LLVM_CTOR_NODISCARD (PR #65418)

[Jon Roelofs via llvm-commits]

================
@@ -307,6 +307,16 @@
 #define LLVM_GSL_POINTER
 #endif
 
+#if LLVM_HAS_CPP_ATTRIBUTE(gnu::visibility)
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jroelofs wrote:

```suggestion
#if LLVM_HAS_CPP_ATTRIBUTE(nodiscard)
```

https://github.com/llvm/llvm-project/pull/65418