[release/7.0.1xx] Fix --use-current-runtime for linux-musl-arm64

[am11]

cc @tmds

[tmds]

This is about ensuring NETCoreSdkPortableRuntimeIdentifier (in <DOTNET_ROOT>/sdk/<version>/Microsoft.NETCoreSdk.BundledVersions.props) is linux-musl-{arch} on musl based platforms.

The fix looks good for Microsoft's portable builds.

We also need to look at making it work for source-build .NET where Rid will be alpine.3.15-x64 for example, and this patch won't work.

cc @crummel @MichaelSimons @ayakael

[am11]

In some places, we are using conditions like:

https://github.com/dotnet/runtime/blob/c8f9f2949a243c411bd05278efab3f5a857cd0c1/src/coreclr/nativeaot/BuildIntegration/Microsoft.DotNet.ILCompiler.SingleEntry.targets#L7

    <OSIdentifier Condition="$(RuntimeIdentifier.StartsWith('linux-musl')) OR $(RuntimeIdentifier.StartsWith('alpine'))">linux-musl</OSIdentifier>

Though it's not ideal (for other musl-based distros), it will cover the officially supported platform matrix.

[marcpopMSFT]

@MichaelSimons is this for rtm?

[MichaelSimons]

Closing in favor of #14647