When building the entire aspnetcore repo (i.e. inside the VMR) desktop msbuild is chosen

[ViktorHofer]

When building aspnetcore inside the VMR, desktop msbuild is being used which is required to build installers. The logic which msbuild engine to use lives here:

aspnetcore/eng/build.ps1

Lines 317 to 323 in eb68e01

	# Don't bother with two builds if just one will build everything. Ignore super-weird cases like
	# "-Projects ... -NoBuildJava -NoBuildManaged -NoBuildNodeJS". An empty `./build.ps1` command will build both
	# managed and native projects.
	$performDesktopBuild = $BuildInstallers -or $BuildNative
	$performDotnetBuild = $BuildJava -or $BuildManaged -or $BuildNodeJS -or `
	($All -and -not ($NoBuildJava -and $NoBuildManaged -and $NoBuildNodeJS)) -or `
	($Projects -and -not ($BuildInstallers -or $specifiedBuildNative))

It might be ok to build the entire repository with desktop msbuild but ideally only the parts that need the desktop engine should build with it. Runtime does that which works really fine. Arcade already has a script that handles shelling out to desktop msbuild.

cc @wtgodbe