[llvm] LangRef: rint, nearbyint: mention that default rounding mode is assumed (PR #77191)

[Andy Kaylor via llvm-commits]

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@@ -15751,7 +15751,9 @@ Semantics:
 """"""""""
 
 This function returns the same values as the libm ``rint`` functions
-would, and handles error conditions in the same way.
+would, and handles error conditions in the same way. The rounding mode
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andykaylor wrote:

> So I guess the more correct thing to say is that LLVM implements it as "what's an exception? these are not the exceptions you are looking for", aka pretending that FP exceptions just do not exist.

Yes, exactly.

https://github.com/llvm/llvm-project/pull/77191