[llvm] [InstSimplify] Fold fsub X, X using known non-NaN/non-Inf facts (PR #200782)

[Simon Pilgrim via llvm-commits]

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RKSimon wrote:

```suggestion
define double @missed_selfsub_consumer(float nofpclass(nan inf) %x, double %scale, double %acc) {
```

https://github.com/llvm/llvm-project/pull/200782