Release fixes for rebuild (#5984)

* Add AOT placeholder files to the JIT package.

This is intended to prevent accidental inclusion in UWP projects.

* Fix CoreCLR package to bring in stable ARM nupkg

Author: ericstj

src/.nuget/Microsoft.NETCore.Jit/win/Microsoft.NETCore.Jit.pkgproj

@@ -19,6 +19,11 @@
   </ItemGroup>
 
   <ItemGroup>
+    <!-- prevent accidental inclusion in AOT projects. -->
+    <File Include="$(PlaceholderFile)">
+      <TargetPath>runtimes/$(PackageTargetRuntime)-aot/native</TargetPath>
+    </File>
+
     <ArchitectureSpecificNativeSymbol Include="@(ArchitectureSpecificNativeFile -> '%(RelativeDir)PDB\%(FileName).pdb')"/>
 
     <AdditionalSymbolPackageExcludes Include="%2A%2A\%2A.dll"/>

src/.nuget/Microsoft.NETCore.Runtime.CoreCLR/Microsoft.NETCore.Runtime.CoreCLR.pkgproj

@@ -15,7 +15,7 @@
     <!-- Declare a runtime dependency on the win8-arm CoreCLR built using the TFS builds -->
     <RuntimeDependency Include="runtime.win8-arm.Microsoft.NETCore.Runtime.CoreCLR">
       <TargetRuntime>win8-arm</TargetRuntime>
-      <Version>1.0.2-$(ExternalExpectedPrerelease)</Version>
+      <Version>1.0.2</Version>
     </RuntimeDependency>
     <!-- ApiSets are only applicable for Windows. 
          Despite the unconditioned package dependency it is constrained by runtime IDs within it's own package -->