Through a chain of updated package references, I'm noticing that this file (ILLink.Descriptors.LibraryBuild.xml) gets automatically created for C# projects that don't use an SDK style format. This impacts a lot of our older code. I've traced the source of these files to System.Diagnostics.DiagnosticSource.

I don't think this causes any harm, but it adds clutter and confusing (developers asking where it came from).

I'm not very familiar with code trimming, but does this file actually need to be included in the output of System.Diagnostics.DiagnosticSource? My specific question is, could this be changed from CONTENT to NONE?

Again, I'm not familiar with the intricacies of code trimming. So if it's required, then I assume "it is what it is" until we can update all our old code. But it would be nice if we didn't get these files auto created.