Consider making native build more fine-grained

[wtgodbe]

Today, we either build all of the native projects, or none of them:

aspnetcore/eng/Build.props

Lines 82 to 87 in d4880ed

	<!-- BuildNative -->
	<ItemGroup Condition=" '$(TargetOsName)' == 'win' AND ('$(TargetArchitecture)' == 'x86' OR '$(TargetArchitecture)' == 'x64' OR '$(TargetArchitecture)' == 'arm64') ">
	<NativeProjects Include="$(RepoRoot)src\**\*.vcxproj" Exclude="@(ProjectToExclude)" AdditionalProperties="Platform=x64" />
	<NativeProjects Include="$(RepoRoot)src\**\*.vcxproj" Exclude="@(ProjectToExclude)" AdditionalProperties="Platform=Win32" />
	<NativeProjects Include="$(RepoRoot)src\**\*.vcxproj" Exclude="@(ProjectToExclude)" AdditionalProperties="Platform=arm64" />
	</ItemGroup>

We should consider making this more fine-grained - today in the VMR, BuildPass 1 builds all of the native projects, then BuildPass2 builds the Hosting Bundle, which re-builds projects like https://github.com/dotnet/aspnetcore/blob/main/src/Servers/IIS/AspNetCoreModuleV2/IISLib/IISLib.vcxproj. It may be possible to save the ANCM-specific native builds for just pass 2, which would cut a couple minutes of build time in the VMR.

[wtgodbe]

Done by recent changes to eng/build.props