Build Visual Studio project with different compilation symbols - visual-studio

Question

I have a VS solution file that contains 1 project. I've been trying to write the project file such that there's a single build target that will build the same project multiple times with different compilation symbols each.
This project is a library that is intended to be used in a mobile Unity project. The library uses #if directives for each platform: Android, iOS and Desktop.
My goal is to build the same project in a different folder with different compilation symbols:
Debug
Android
Lib.DLL ("UNITY_ANDROID" compilation symbols)
iOS
Lib.DLL ("UNITY_IPHONE" compilation symbols)
Standalone
Lib.DLL ("" compilation symbols)
Release
Android
Lib.DLL ("UNITY_ANDROID" compilation symbols)
iOS
Lib.DLL ("UNITY_IPHONE" compilation symbols)
Standalone
Lib.DLL ("" compilation symbols)
Originally, I would manually edit the project file, set the compilation symbols, build, rinse and repeat. It kinda worked, but it was messy.
I then discovered that there's a way to do this in a single project file, but I have yet to figure out how. I've tried this with no success.
To give a little more context, I'm using CakeBuild to build the project and this is how I'm calling the project target:
DotNetBuild("./Lib/Lib.sln", settings => settings.WithTarget("Build"));
I am totally OK with calling that line multiple times with different configurations or targets, but I have not found a way to change the compilation symbols.
Here's a snippet of the project file:
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
<PropertyGroup>
<Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
<Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
<ProjectGuid>{CF15E877-F285-496B-B748-C9A666D97D0F}</ProjectGuid>
<OutputType>Library</OutputType>
<AppDesignerFolder>Properties</AppDesignerFolder>
<RootNamespace>JsonDotNet</RootNamespace>
<AssemblyName>JsonDotNet</AssemblyName>
<TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
<FileAlignment>512</FileAlignment>
<TargetFrameworkProfile />
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)' == 'Debug-Android' ">
<DebugSymbols>true</DebugSymbols>
<DebugType>full</DebugType>
<Optimize>false</Optimize>
<OutputPath>bin\Debug\Android\lib\net35\</OutputPath>
<DefineConstants>UNITY_ANDROID</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)' == 'Debug-iOS' ">
<DebugSymbols>true</DebugSymbols>
<DebugType>full</DebugType>
<Optimize>false</Optimize>
<OutputPath>bin\Debug\iOS\lib\net35\</OutputPath>
<DefineConstants>UNITY_IPHONE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)' == 'Debug-x86' ">
<DebugSymbols>true</DebugSymbols>
<DebugType>full</DebugType>
<Optimize>false</Optimize>
<OutputPath>bin\Debug\iOS\lib\net35\</OutputPath>
<DefineConstants></DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)' == 'Release-Android' ">
<DebugType>pdbonly</DebugType>
<Optimize>true</Optimize>
<OutputPath>bin\Release\Android\lib\net35\</OutputPath>
<DefineConstants>UNITY_ANDROID</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)' == 'Release-iOS' ">
<DebugType>pdbonly</DebugType>
<Optimize>true</Optimize>
<OutputPath>bin\Release\iOS\lib\net35\</OutputPath>
<DefineConstants>UNITY_IPHONE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)' == 'Release-x86' ">
<DebugType>pdbonly</DebugType>
<Optimize>true</Optimize>
<OutputPath>bin\Release\iOS\lib\net35\</OutputPath>
<DefineConstants></DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<ItemGroup>
<ProjectToBuild Include="..\Lib.sln">
<Properties>Configuration=Debug-iOS</Properties>
</ProjectToBuild>
<ProjectToBuild Include="..\Lib.sln">
<Properties>Configuration=Debug-Android</Properties>
</ProjectToBuild>
<ProjectToBuild Include="..\Lib.sln">
<Properties>Configuration=Debug-x86</Properties>
</ProjectToBuild>
<ProjectToBuild Include="..\Lib.sln">
<Properties>Configuration=Release-iOS</Properties>
</ProjectToBuild>
<ProjectToBuild Include="..\Lib.sln">
<Properties>Configuration=Release-Android</Properties>
</ProjectToBuild>
<ProjectToBuild Include="..\Lib.sln">
<Properties>Configuration=Release-x86</Properties>
</ProjectToBuild>
</ItemGroup>
<Target Name="Build">
<MSBuild Projects="#(ProjectToBuild)" BuildInParallel="true" />
</Target>
When I run this, only Debug Android is built. I've also tried including the platform in the condition (i.e. Condition=" '$(Configuration)|$(Platform)' == 'Debug|iOS' ") with the same results.