Allow building runtime.native.System.IO.Ports for community-supported architectures by default

### Description

`runtime.native.System.IO.Ports` should be built by default, even for community-supported platforms.

Currently downstream distributors like https://github.com/loongson/dotnet have to [explicitly patch the project file](https://github.com/loongson/dotnet/commit/0e78970908853ac291da815867dd17cb912a3fb9) to get it built, which is suboptimal.

https://github.com/dotnet/runtime/pull/106850 did try to fix it, but that breaks Microsoft builds since the overall `runtime.native.System.IO.Ports` package have dependencies on packages targeting every platform, and those which are community-supported won't be built.

Can we at least have the package built by default, but not referenced by `runtime.native.System.IO.Ports`? That way people can at the very least consume it using conditional PackageReference:

```xml

```

### Reproduction Steps

Build dotnet runtime for community-supported architecture, like `linux-loongarch64`.

### Expected behavior

Have runtime.linux-loongarch64.runtime.native.System.IO.Ports.nupkg in the artifacts.

### Actual behavior

The nupkg does not exist, and one will need to use other workarounds to consume the package.

### Regression?

_No response_

### Known Workarounds

_No response_

### Configuration

_No response_

### Other information

_No response_