Remove System.Runtime.Intrinsics for .NET Core 2.1

[eerhardt]

• Remove System.Runtime.Intrinsics from Microsoft.NETCore.App.
• Rename to System.Runtime.Intrinsics.Experimental
• Create a standalone nupkg.

See https://github.com/dotnet/corefx/issues/27486 for more information.

[sdmaclea]

LGTM

[fiigii]

Thanks!

[sdmaclea]

@tannergooding Please cc me on test changes to add ref.

[ahsonkhan]

@eerhardt, good to merge?

[tannergooding]

@sdmaclea, could you clarify your request?

[eerhardt]

good to merge?

I'd like for this to get at least a cursory look from @ericstj or @weshaggard first to ensure the pkg stuff looks right.

[sdmaclea]

@tannergooding I am assuming the tests in coreclr will need to be updated to add a ref to the new external package. I also assume the ne wpackage must be uploaded to nuget before coreclr can reference it. So when you create the change in coreclr to pick this up, I'd like to be cc'd, so that I know it is ready.

[eerhardt]

@sdmaclea - I'm not very familiar with coreclr's tests, but don't they just compile directly against System.Private.CoreLib? (I have no idea, just my assumption)

See https://github.com/dotnet/coreclr/blob/a16a8a852077b0c471cf12ef75dc5e8a41333533/tests/override.targets#L21

[sdmaclea]

@eerhardt The Arm64 coreclr tests did not compile w/o corefx HW Intrinsic ref dll. They are currently disabled in CoreCLR because API is not published.

[AndyAyersMS]

CoreCLR tests can be set up to compile against corelib directly, but it's not commonly done.

So when this CoreFX change hits CoreCLR likely the test builds will need fixes.

[sdmaclea]

@AndyAyersMS If you have instructions/sample of a test building directly against corelib, it would be helpful as we add lots of HW Intrinsic APIs. (Eliiminates the circular dependency implement in coreclr, build ref in corefx, build tests in coreclr). The tests shouldn't probably check in that way, but it would make dev life simpler.

[AndyAyersMS]

I think the magic is to add:

<ReferenceSystemPrivateCoreLib>true</ReferenceSystemPrivateCoreLib>

to the csproj. For example look at Interop\ICastable\Castable.csproj. Not sure if this causes other complications.

[ViktorHofer]

Am I the only one who can't build anymore because of the renamed package?

C:\git\corefx\Tools\Packaging.targets(1231,5): error : Error when creating nuget packed package from C:\git\corefx\bin\
packages\Debug\specs\Microsoft.Private.CoreFx.NETCoreApp.nuspec. System.IO.DirectoryNotFoundException: Could not find a
 part of the path 'C:\git\corefx\src\System.Runtime.Intrinsics\ref'. [C:\git\corefx\pkg\Microsoft.Private.CoreFx.NETCor
eApp\Microsoft.Private.CoreFx.NETCoreApp.pkgproj]

[eerhardt]

I'd suggest git clean -xdf and build again.