How to use MSBuild to build multiple platforms

I am using Visual Studio online build with an MSBuild task. I currently have the following MSBuild Arguments fed to my task:

/p:Configuration=Release;AppxBundle=Always;AppxBundlePlatforms="x86|x64|ARM";AppxPackageDir="$(Build.BinariesDirectory)\AppxPackages\\";UapAppxPackageBuildMode=StoreUpload

This creates my application in x86, x64 and ARM. It creates Release version of the libraries in x86 BUT creates Debug version of my libraries in x64 and ARM.

When my .appxupload package is creates it fails Windows Certification tests because my libraries are built in debug.

How can I make MSBuild build for all 3 configurations. My guess is because I haven't provided a /platform configuration. How do I provide this configuration for 3 platforms?

I have tried platform="x86|x64|ARM" but it returned an error

For a standard project file there's no way to do this in a single command. Either use multiple commands to build the project for each platform/configuration combination needed, or use a 'master' build file which does the same for you, something like:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" DefaultTargets="FullRebuild">
  <Target>
    <ItemGroup>
      <Configurations Include="Debug;Release"/>
      <Platforms Include="x86;x64;ARM"/>
      <ConfigAndPlatform Include="@(Configurations)">
        <Platform>%(Platforms.Identity)</Platform>
      </ConfigAndPlatform>
    </ItemGroup>
    <MSBuild Projects="myproject.sln" Targets="Build"
             Properties="Configuration=%(ConfigAndPlatform.Identity);Platform=%(ConfigAndPlatform.Platform)"/>
  </Target>
</Project>