MSBuild Additional DefineConstants via property

test.csproj

<?xml version="1.0" encoding="utf-8"?>
<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Target Name="DisplayMessages">
    <Message Text="Configuration: $(Configuration)" />
    <Message Text="DefineConstants: $(DefineConstants)" />
    <Message Text="AdditionalDefineConstants: $(AdditionalDefineConstants)" />
  </Target>
  <PropertyGroup>
    <DefineConstants>TEST</DefineConstants> <!-- this DefineConstants is optional -->
    <DefineConstants Condition=" '$(AdditionalDefineConstants)' != '' ">$(DefineConstants);$(AdditionalDefineConstants)</DefineConstants>
  </PropertyGroup>
</Project>

test.sh

msbuild test.csproj /t:DisplayMessages /p:Configuration=Release /p:AdditionalDefineConstants="Additional_Define_Constants_Here"