[llvm] [IRBuilder] Refactor FMF interface (PR #121657)

[Nikita Popov via llvm-commits]

================
@@ -87,6 +87,20 @@ class IRBuilderCallbackInserter : public IRBuilderDefaultInserter {
   }
 };
 
+/// This provides a helper for copying FMF from an instruction or setting
+/// specified flags.
+struct FMFSource final {
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nikic wrote:

```suggestion
struct FMFSource {
```
Don't need final for non-virtual classes.

https://github.com/llvm/llvm-project/pull/121657