Audit usage of build tags

[dave-tucker]

What would you like to be added?

While working on #1390 I fell into a trap.
Build tags are currently being used to gate:

• bcc
• libbpf
• gpu
• darwin

Due to the way CI is set up (lint for example) and how tooling like go lint and go vet work it's quite possible that the linters aren't being run on all files - meaning that reviewers will need to be ultra cautious on vetting changes to these files.

Why is this needed?

To ensure everything builds and lints properly it would be a good idea to drop all unnecessary build tags.

Ideally that would include the darwin stubs as this seems to create a lot of work for very little gain - i.e you'd be better building inside a Linux Container on macOS (given this software is macOS specific) than having to maintain a sprawl of stub files.