[XamlC] fix release builds of Xaml Unit Tests

.nuspec/Xamarin.Forms.Debug.targets

@@ -66,7 +66,8 @@
 			Assembly = "$(IntermediateOutputPath)$(TargetFileName)"
 			ReferencePath = "@(ReferencePath)"
 			Verbosity = "4"
-			DebugSymbols = "$(DebugSymbols)" />
+			DebugSymbols = "$(DebugSymbols)"
+			DebugType = "$(DebugType)"/>
 	</Target>
 
 	<Target Name="XamlC">