build.proj

<?xml version="1.0" encoding="utf-8"?>
<Project
  xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
  DefaultTargets="Build">
  
  <ItemGroup>
    <Solution Include="build.sln" >      
        <Properties>Configuration=Debug;Platform=Win32</Properties>
    </Solution>
    <Solution Include="build.sln" >
        <Properties>Configuration=Release;Platform=Win32</Properties>
    </Solution>
    <Solution Include="build.sln" >
        <Properties>Configuration=Debug;Platform=x64</Properties>
    </Solution>
    <Solution Include="build.sln" >
        <Properties>Configuration=Release;Platform=x64</Properties>
    </Solution>
  </ItemGroup>
  
  <Target Name="Clean">
    <!-- Clean the solutions -->
    <Message Importance="high" Text="Cleaning all projects..." ContinueOnError="true" />
    <MSBuild
      Projects="@(Solution)"
      Targets="Clean"
      BuildInParallel="true" />
  </Target>

  <Target Name="Build" DependsOnTargets="Clean">
    <Message Importance="high" Text="Building all versions of the projects..." />
    <MSBuild
      Projects="@(Solution)"
      Targets="Build"
      BuildInParallel="true" />
  </Target>
</Project>