Don't enable runtime linking in debug builds

It seems `$(AndroidIncludeDebugSymbols)` isn't defined yet by the time
`src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets`
is evaluated, so we need to move `$(_AndroidEnableNativeRuntimeLinking)`
to src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets in
order to disable linking in Debug builds.

Author: grendello

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets

@@ -52,9 +52,6 @@
         When changing this default, change the value of `DefaultZipAlignment` in `src/Xamarin.Android.Build.Tasks/Tasks/AndroidZipAlign.cs` as well
     -->
     <AndroidZipAlignment Condition=" '$(AndroidZipAlignment)' == '' ">16</AndroidZipAlignment>
-
-    <!-- Native runtime -->
-    <_AndroidEnableNativeRuntimeLinking Condition=" '$(_AndroidEnableNativeRuntimeLinking)' == '' and '$(AndroidIncludeDebugSymbols)' != 'true' ">true</_AndroidEnableNativeRuntimeLinking>
   </PropertyGroup>
 
   <!--  User-facing configuration-specific defaults -->

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -327,6 +327,9 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
   <AndroidEnableMarshalMethods Condition=" '$(AndroidEnableMarshalMethods)' == '' ">False</AndroidEnableMarshalMethods>
   <_AndroidUseMarshalMethods Condition=" '$(AndroidIncludeDebugSymbols)' == 'True' ">False</_AndroidUseMarshalMethods>
   <_AndroidUseMarshalMethods Condition=" '$(AndroidIncludeDebugSymbols)' != 'True' ">$(AndroidEnableMarshalMethods)</_AndroidUseMarshalMethods>
+
+  <!-- Native runtime linking during app build -->
+  <_AndroidEnableNativeRuntimeLinking Condition=" '$(_AndroidEnableNativeRuntimeLinking)' == '' and '$(AndroidIncludeDebugSymbols)' != 'true' ">true</_AndroidEnableNativeRuntimeLinking>
 </PropertyGroup>
 
 <!-- Do not resolve from the GAC under any circumstances in Mobile -->