Steps to reproduce:

1. Open attached project using file explorer and set read-only to the following files:
Assets\WSA\ARM\MicStreamerSelector.dll
Assets\WSA\x64\MicStreamerSelector.dll
Assets\WSA\x86\MicStreamerSelector.dll
Assets\x64\MicStreamerSelector.dll
Assets\x86\MicStreamerSelector.dll
2. Open project in Unity and try to build Universal build
3. Build fails with the following error:
UnauthorizedAccessException: Access to the path "Temp\StagingArea\New Unity Project.Windows\Data\Managed\Plugins\ARM\MicStreamSelector.dll" is denied.
System.IO.File.Delete (System.String path) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/File.cs:179)
System.IO.Directory.RecursiveDelete (System.String path) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/Directory.cs:195)
System.IO.Directory.RecursiveDelete (System.String path) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/Directory.cs:190)
System.IO.Directory.RecursiveDelete (System.String path) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/Directory.cs:190)
System.IO.Directory.Delete (System.String path, Boolean recursive) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/Directory.cs:205)
Utility.DeleteDirectory (System.String path) (at C:/buildslave/unity/build/PlatformDependent/WinRT/SharedSources/CSharp/Utility.cs:322)
PostProcessWinRT.MoveDataManagedToRoot () (at C:/buildslave/unity/build/PlatformDependent/WinRT/SharedSources/CSharp/PostProcessWinRT.cs:477)
PostProcessUniversal81.MoveDataManagedToRoot () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/PostProcessUniversal81.cs:97)
PostProcessWinRT.Process () (at C:/buildslave/unity/build/PlatformDependent/WinRT/SharedSources/CSharp/PostProcessWinRT.cs:125)
PostProcessUniversal81.Process () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/PostProcessUniversal81.cs:45)
UnityEditor.WSA.BuildPostprocessor.PostProcess (BuildPostProcessArgs args) (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/ExtensionModule.cs:150)
UnityEditor.PostprocessBuildPlayer.Postprocess (BuildTarget target, System.String installPath, System.String companyName, System.String productName, Int32 width, Int32 height, System.String downloadWebplayerUrl, System.String manualDownloadWebplayerUrl, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.BuildReporting.BuildReport report) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:186)
UnityEditor.BuildPlayerWindow:BuildPlayerAndRun()