[llvm] [NFC] update doc comment on `setLoopEstimatedTripCount` (PR #178091)

[Joel E. Denny via llvm-commits]

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@@ -359,7 +359,19 @@ getLoopEstimatedTripCount(Loop *L,
 /// - Set the branch weight metadata of \p L to reflect that \p L has an
 ///   estimated \p EstimatedTripCount iterations and has
 ///   \c *EstimatedLoopInvocationWeight exit weight through the loop's latch.
-/// - If \p EstimatedTripCount is zero, zero the branch weights.
+/// - If \p EstimatedTripCount is zero, set the backedge weight to 0 and exit
+///   edge to 1. The \EstimatedTripCount is relative to the original loop entry,
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jdenny-ornl wrote:

```suggestion
///   edge to 1. The \p EstimatedTripCount is relative to the original loop entry,
```

https://github.com/llvm/llvm-project/pull/178091