By default, go binaries currently include only a
Go build-id, but it is also useful to include a
Gnu build-id.

Providing a Gnu build-id in a binary enables more robust
support for Gnu profiling, tracing, and debugging tools.
For example, it prevents an ugly scenario where the wrong
symbols are used when analyzing a profile that was captured
prior to a recent install of that binary.

Like all build-ids, the Gnu build-id must be unique.
Ideally it should also be deterministic, as that supports
repeatable builds, which in turn enable supply chain integrity
validation, equivalency testing, etc.

The Go build-id has both properties: unique and deterministic.
Here we generate a Gnu build-id based on the Go build-id,
inheriting those 2 properties.

We hope to make this an automatic behavior of go build in the
future, reducing overhead and risk.  But for now, this approach
approximates the required certainty of uniqueness (including
differentiating between builds that use the same source code
but different versions of go or statically linked libraries).