Try different MSBuild things to make build work (#17427)

Fixes #17418

Author: pranavkm

src/Components/Blazor/Build/src/ReferenceFromSource.props

@@ -20,16 +20,23 @@
     <Reference Include="Microsoft.AspNetCore.Blazor.Mono" />
   </ItemGroup>
 
+  <Target Name="_BuildBlazorBuildProject" BeforeTargets="ResolveProjectReferences">
+    <!--
+      The Blazor.Build project cross-compiles and we need the output of all TFMs to be available in the build output.
+      We can't represent this in any good way using ProjectReference elements, but we can try and build it instead.
+    -->
+    <MSBuild Projects="$(MSBuildThisFileDirectory)Microsoft.AspNetCore.Blazor.Build.csproj" />
+  </Target>
+
   <!-- This is used as a P2P when building the repo. Normal Blazor projects will get this as a reference through the Blazor.Build package -->
   <ItemGroup>
     <!-- Ensures these projects are built before the consuming project, but without
          adding a runtime dependency on the .dll (to be equivalent to a <PackageDependency>
          given that the packed version of this project wouldn't add a .dll reference) -->
     <ProjectReference Include="$(MSBuildThisFileDirectory)Microsoft.AspNetCore.Blazor.Build.csproj">
       <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
-      <!-- Optimization. Do not require framework compatibility between these projects. -->
       <SkipGetTargetFrameworkProperties>true</SkipGetTargetFrameworkProperties>
-      <UndefineProperties>TargetFramework</UndefineProperties>
+      <Properties>TargetFramework=$(DefaultNetCoreTargetFramework)</Properties>
     </ProjectReference>
     <ProjectReference Include="$(MSBuildThisFileDirectory)..\..\DevServer\src\Microsoft.AspNetCore.Blazor.DevServer.csproj">
       <ReferenceOutputAssembly>false</ReferenceOutputAssembly>