I get this error when building an MVC project in a solution. No references to those files exists in my solution at all.
C:\\Program Files (x86)\\MSBuild\\14.
I used to have the same issue but I just removed Microsoft.CodeDom.Providers.DotNetCompilerPlatform and then installed 1.0.0. I found that after that it all looks good.
Microsoft.CodeDom.Providers.DotNetCompilerPlatform