Add new file to project file to fix build.

src/framework/GuiUnit_xammac_mobile.csproj

@@ -358,6 +358,7 @@
     <Compile Include="GuiUnit\XmlTestListener.cs" />
     <Compile Include="GuiUnit\AdditionalAsserts.cs" />
     <Compile Include="GuiUnit\GtkMainLoopIntegration.cs" />
+    <Compile Include="Constraints\CollectionSupersetConstraint.cs" />
   </ItemGroup>
   <ItemGroup>
     <Folder Include="Properties\" />