Notice to out of tree targets: TargetLowering::hasBitPreservingFPLogic is being removed

In ⚙ D142567 DAG: Remove hasBitPreservingFPLogic I’m going to be removing this target hook which changes the default behavior from disabling combines to turn integer bit operations into fabs or fneg. This will now be done if the operation is legal. This was a leftover from when there was confusion around fneg’s behavior since the IR represented it as a special case of fsub. These are bit preserving by definition, and if a target had an fneg or fabs instruction which is not bit preserving, it’s not legal to select from the IEEE operations.

This kind of notice probably warrants (a) a release note entry, (b) a post in the Announcements section, which is intended to be a category that downstream projects can watch.

I wasn’t sure about the category; the announcements description sounds like a higher level category to me than things like this

I moved this to the LLVM Project topic, which is the right place for announcements like this.