Address UX issue when building with a Portable Target RID

https://github.com/dotnet/sdk/pull/40843#issuecomment-2123388322 highlights that while source-building the VMR with a portable RID implies a portable build, merely naming something doesn't automatically imbue it with the associated properties.

To achieve a functioning portable build, it necessitates a specific setup, including the use of a portable build property and building on the oldest glibc possible, such as CentOS 8 rather than CentOS 9. Without these measures, we might end up with a build that, although labeled as portable, doesn't perform as one.

Two questions then arise:

- Should we automatically enable portable-build mode when a portable RID is specified?
- Should we implement a check to prevent building with a portable RID if the glibc version in use is newer than our baseline?

In general, in answering and addressing these questions, we will improve the UX experience of providing a portable target RID to the build.