Bring back ExtraDefine

Author: AArnott

LibGit2Sharp.Tests/LibGit2Sharp.Tests.csproj

@@ -25,4 +25,5 @@
     <PackageReference Include="xunit.runner.msbuild" Version="2.0.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
   </ItemGroup>
+  <Import Project="..\LibGit2Sharp\ExtraDefine.targets" />
 </Project>

LibGit2Sharp/ExtraDefine.targets

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <!-- Add extra defines to DefineConstants. -->
+  <PropertyGroup>
+    <DefineConstants Condition=" '$(ExtraDefine)' != '' ">$(DefineConstants);$(ExtraDefine)</DefineConstants>
+  </PropertyGroup>
+</Project>

LibGit2Sharp/LibGit2Sharp.csproj

@@ -38,6 +38,7 @@
     <PackageReference Include="System.IO.UnmanagedMemoryStream" Version="4.0.1" Condition=" '$(TargetFramework)' == 'netstandard1.3' " />
   </ItemGroup>
   <Import Project="CodeGenerator.targets" />
+  <Import Project="ExtraDefine.targets" />
   <Target Name="SetNuSpecProperties" BeforeTargets="GenerateNuspec" DependsOnTargets="GetBuildVersion">
     <PropertyGroup>
       <PackageIconUrl>https://github.com/libgit2/libgit2sharp/raw/$(GitCommitIdShort)/square-logo.png</PackageIconUrl>