[tests/mscorlib] Fix template. (#897)

tests/bcl-test/mscorlib/mscorlib-split.csproj.template

@@ -12,6 +12,7 @@
     <AssemblyName>mscorlibtests#SPLIT#</AssemblyName>
     <NoWarn>168,169,219,414,612,618,649,672</NoWarn>
     <TargetFrameworkIdentifier>Xamarin.iOS</TargetFrameworkIdentifier>
+    <DefineConstants>XAMCORE_2_0;XAMCORE_3_0</DefineConstants>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
     <DebugSymbols>True</DebugSymbols>