[llvm] [ValueTracking] Merge `cannotBeOrderedLessThanZeroImpl` into `computeKnownFPClass` (PR #76360)

[Matt Arsenault via llvm-commits]

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@@ -332,6 +332,12 @@ struct KnownFPClass {
 
   void knownNot(FPClassTest RuleOut) {
     KnownFPClasses = KnownFPClasses & ~RuleOut;
+    if (isKnownNever(fcNan) && !SignBit) {
+      if (isKnownNever(OrderedLessThanZeroMask | fcNegZero))
+        SignBit = false;
+      else if (isKnownNever(OrderedGreaterThanZeroMask | fcPosZero))
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arsenm wrote:

```suggestion
      else if (isKnownNever(fcPositive))
```

https://github.com/llvm/llvm-project/pull/76360