Enable building projects during BuildPass=2 in dotnet/runtime (#112201)

* Enable building projects during BuildPass=2 in dotnet/runtime

* Only provide the DotNetBuildPass=2 variant when actually in that build pass

* Use TargetOS/Arch instead (we don't have TargetRID available at this time in Build.proj)

Author: jkoritzinsky

eng/Build.props

@@ -5,5 +5,7 @@
   </PropertyGroup>
   <ItemGroup>
     <ProjectToBuild Include="$(RepoRoot)Build.proj" />
+    <!-- dotnet/runtime controls which projects run in which passes through our DefaultSubsets settings in eng/Subsets.props -->
+    <ProjectToBuild Include="$(RepoRoot)Build.proj" DotNetBuildPass="2" Condition="'$(DotNetBuildPass)' == '2'" />
   </ItemGroup>
 </Project>

eng/Subsets.props

@@ -69,7 +69,7 @@
     <DefaultSubsets Condition="'$(DotNetBuildMonoCrossAOT)' == 'true'">mono+packs</DefaultSubsets>
 
     <!-- In the Win-x86 BuildPass2 job in the VMR, we want to build the cross-OS DACs and pack them. -->
-    <DefaultSubsets Condition="'$(DotNetBuildPass)' == '2' and '$(TargetRid)' == 'win-x86'">crossdacpack</DefaultSubsets>
+    <DefaultSubsets Condition="'$(DotNetBuildPass)' == '2' and '$(TargetOS)' == 'windows' and '$(TargetArchitecture)' == 'x86'">crossdacpack</DefaultSubsets>
   </PropertyGroup>
 
   <PropertyGroup>