Add a hook for the location of installers passed from phase 1 into phase 2

Author: jkoritzinsky

Directory.Build.props

@@ -247,6 +247,8 @@
     <!-- Allow overriding the public base URL for Unified Build scenarios to pull assets from a local build. -->
     <PublicBaseURL Condition="'$(PublicBaseURL)' == ''">https://dotnetbuilds.azureedge.net/public/</PublicBaseURL>
     <InternalBaseURL>https://dotnetbuilds.azureedge.net/internal/</InternalBaseURL>
+    <!-- Allow overriding where installers are pulled in from previously completed jobs in Unified Build scenarios. -->
+    <CrossArchitectureInstallerBasePath Condition="'$(CrossArchitectureInstallerBasePath)' == ''">$(InstallersOutputPath)</CrossArchitectureInstallerBasePath>
   </PropertyGroup>
 
   <!-- Try various places to find the runtime. It's either released (use official version),

src/Installers/Windows/WindowsHostingBundle/WindowsHostingBundle.wixproj

@@ -104,17 +104,17 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <SharedFxInstallers Include="$(InstallersOutputPath)$(RuntimeInstallerBaseName)-$(SharedFxMsiVersion)-win-x64.msi">
+    <SharedFxInstallers Include="$(CrossArchitectureInstallerBasePath)$(RuntimeInstallerBaseName)-$(SharedFxMsiVersion)-win-x64.msi">
       <TargetPlatform>x64</TargetPlatform>
       <BundleNameProperty>SharedFxRedistInstallerx64</BundleNameProperty>
       <Version>$(SharedFxPackageVersion)</Version>
     </SharedFxInstallers>
-    <SharedFxInstallers Include="$(InstallersOutputPath)$(RuntimeInstallerBaseName)-$(SharedFxMsiVersion)-win-x86.msi">
+    <SharedFxInstallers Include="$(CrossArchitectureInstallerBasePath)$(RuntimeInstallerBaseName)-$(SharedFxMsiVersion)-win-x86.msi">
       <TargetPlatform>x86</TargetPlatform>
       <BundleNameProperty>SharedFxRedistInstallerx86</BundleNameProperty>
       <Version>$(SharedFxPackageVersion)</Version>
     </SharedFxInstallers>
-    <SharedFxInstallers Include="$(InstallersOutputPath)$(RuntimeInstallerBaseName)-$(SharedFxMsiVersion)-win-arm64.msi">
+    <SharedFxInstallers Include="$(CrossArchitectureInstallerBasePath)$(RuntimeInstallerBaseName)-$(SharedFxMsiVersion)-win-arm64.msi">
       <TargetPlatform>arm64</TargetPlatform>
       <BundleNameProperty>SharedFxRedistInstallerarm64</BundleNameProperty>
       <Version>$(SharedFxPackageVersion)</Version>