Build.Cleanall.proj

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <ItemGroup>
      <ExternalExclude Include="$(MSBuildStartupDirectory)\External Projects\**\\*.*"></ExternalExclude>
    </ItemGroup>
    <ItemGroup>
      <ProjectFiles Include="$(MSBuildStartupDirectory)\**\*.pdb" Exclude="@(ExternalExclude)" />
      <ProjectFiles Include="$(MSBuildStartupDirectory)\**\obj\*.*" Exclude="@(ExternalExclude)" />
      <ProjectFiles Include="$(MSBuildStartupDirectory)\**\bin\*.*" Exclude="@(ExternalExclude)" />
    </ItemGroup>  
    <Target Name="build">
      <Delete Files="@(ProjectFiles)" />
    </Target>
</Project>