[VMR] Pass target architecture on Windows

We didn't pass an explicit architecture so it always used the host one, even for arm64/x86 builds.

Contributes to dotnet/source-build#4292

Author: akoeplinger

eng/pipelines/templates/jobs/vmr-build.yml

@@ -238,7 +238,7 @@ jobs:
 
   - ${{ if eq(parameters.targetOS, 'windows') }}:
     - script: |
-        call $(sourcesPath)\build.cmd -ci -cleanWhileBuilding -prepareMachine ${{ parameters.extraProperties }}
+        call $(sourcesPath)\build.cmd -ci -cleanWhileBuilding -prepareMachine /p:TargetArchitecture=${{ parameters.targetArchitecture }} ${{ parameters.extraProperties }}
       displayName: Build
 
   - ${{ else }}: