bcc: 0.7.0 -> 0.8.0

[dtzWill]

Motivation for this change

Fix compat w/kernel 5.0, probably other things too (?).

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

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[dtzWill]

Looks like bcc was broken when the BPF target stopped being included in LLVM (see ff22d90 for related fallout re:dropping AMDGPU target). Will issue PR to re-add it / discuss, shortly.