To reproduce:
1. Open attached repro project
2. Build for Windows Phone 8.1
3. Notice the errors in console:

Error building Player: Exception: Failed to run Reference Rewriter with cmdline --target="Temp/StagingArea\Assembly-CSharp-firstpass.dll" --framework="C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\WindowsPhoneApp\v8.1" --platform="C:\Program Files (x86)\Windows Phone Kits\8.1\References\CommonConfiguration\Neutral\Windows.winmd" --support="Temp/StagingArea\WinRTLegacy.dll" --supportpartialns=Unity.Partial --system=System --dbg=pdb --alt=System.Xml.Serialization --ignore=System.IConvertible,mscorlib.[Temp/StagingArea\Assembly-CSharp-firstpass.dll]
Catastrophic failure while running rrw: System.ArgumentException: Invalid type name!
Parameter name: Windows.Foundation.Collections.IVector`1<System.Int32
at Unity.ReferenceRewriter.TypeAliases.GetTemplateArguments(String type)
at Unity.ReferenceRewriter.TypeAliases.AreAliases(String typeA, String typeB)
at Unity.ReferenceRewriter.TypeAliases.AreAliases(String typeA, String typeB)
at Unity.ReferenceRewriter.TypeAliases.AreAliases(String typeA, String typeB)
at Unity.ReferenceRewriter.RewriteTypeReferences.AreSame(TypeReference a, TypeReference b)
at Unity.ReferenceRewriter.RewriteTypeReferences.AreSame(Collection`1 a, Collection`1 b)
at Unity.ReferenceRewriter.RewriteTypeReferences.GetMethodDefinition(IEnumerable`1 methods, MethodReference reference)
at Unity.ReferenceRewriter.RewriteTypeReferences.ResolveManually(MethodReference method)
at Unity.ReferenceRewriter.RewriteTypeReferences.Visit(MethodReference method, String referencingEntityName)
at Unity.ReferenceRewriter.ReferenceDispatcher.Visit(MethodReference method, String referencingEntityName)
at Unity.ReferenceRewriter.ReferenceDispatcher.DispatchMethodBody(MethodBody body)
at Unity.ReferenceRewriter.ReferenceDispatcher.DispatchMethod(MethodDefinition method)
at Unity.ReferenceRewriter.ReferenceDispatcher.DispatchMethods(TypeDefinition type)
at Unity.ReferenceRewriter.ReferenceDispatcher.Dispatch()
at Unity.ReferenceRewriter.RewriteOperation.Execute(RewriteContext context)
at Unity.ReferenceRewriter.Program.Main(String[] args)

These errrors are caused by the native plugin that uses an IMap<IMap<IVector<int>^, IVector<int>^>^, IMap<IVector<int>^, IVector<int>^>^>^

Workaround: build with 'C# projects' enabled