Fix pretest build sequencing

src/libraries/pretest.proj

@@ -4,13 +4,24 @@
     <TraversalGlobalProperties>BuildAllProjects=true</TraversalGlobalProperties>
   </PropertyGroup>
 
+  <!-- Explicitly build the runtime.depproj project first to correctly set up the testhost. -->
+  <ItemGroup>
+    <RuntimeProject Include="restore\runtime\runtime.depproj" />
+    <ProjectReference Include="@(RuntimeProject)" Condition="'$(MSBuildRestoreSessionId)' != ''" />
+  </ItemGroup>
+
   <ItemGroup>
-    <!-- Explicitly include the runtime.depproj project here to correctly set up the testhost. -->
-    <ProjectReference Include="restore\runtime\runtime.depproj" />
     <!-- This is necessary as inside VS project references that aren't part of the sln aren't built. -->
     <ProjectReference Include="$(CommonTestPath)CoreFx.Private.TestUtilities\CoreFx.Private.TestUtilities.csproj" />
   </ItemGroup>
 
+  <Target Name="RestoreTestHost"
+          BeforeTargets="Build">
+    <MSBuild Targets="Build"
+             Projects="@(RuntimeProject)"
+             Properties="$(TraversalGlobalProperties)" />
+  </Target>
+
   <!-- Microsoft.XmlSerializer.Generator should not be marked as a platform item and be copy-local instead. -->
   <Target Name="CollectSharedFrameworkRuntimeFiles"
           Condition="'$(PlatformManifestFile)' != '' and '$(BuildingNETCoreAppVertical)' == 'true'">
@@ -30,7 +41,7 @@
   <Target Name="GenerateFileVersionProps"
           DependsOnTargets="CollectSharedFrameworkRuntimeFiles"
           Condition="'$(PlatformManifestFile)' != '' and '$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'"
-          AfterTargets="Build">
+          AfterTargets="RestoreTestHost">
     <GenerateFileVersionProps Files="@(SharedFrameworkRuntimeFiles)"
                               PackageId="Microsoft.NETCore.App"
                               PackageVersion="$(ProductVersion)"
@@ -47,7 +58,7 @@
   <UsingTask TaskName="GenerateTestSharedFrameworkDepsFile" AssemblyFile="$(InstallerTasksAssemblyPath)"/>
   <Target Name="GenerateTestSharedFrameworkDepsFile"
           Condition="'$(BinplaceTestSharedFramework)' == 'true' and '$(BuildTargetFramework)' == '$(NetCoreAppCurrent)'"
-          AfterTargets="Build">
+          AfterTargets="RestoreTestHost">
     <GenerateTestSharedFrameworkDepsFile SharedFrameworkDirectory="$(NETCoreAppTestSharedFrameworkPath)"
                                          RuntimeGraphFiles="$(RuntimeIdGraphDefinitionFile)"
                                          TargetRuntimeIdentifier="$(PackageRID)" />