I had to change the WebAPI and MVC project files to not build views:
<MvcBuildViews>false</MvcBuildViews>This resolved my TFS 2015 Build server error with roslyn. Still not sure why csc.exe was copied to \bin\csc.exe, yet the publish process was looking for \bin\Roslyn\csc.exe...couldn't find the transformation causing that discrepancy.