`bbctl` formula fails to build on some linux systems

failure logs from @jasdeep.s.basra

that error message looks something like

/tmp/go-build/cgo-gcc-prolog:60:(.text+0x25): undefined reference to `__res_search`

this error message matches this homebrew thread, let's dig in: https://github.com/Homebrew/homebrew-core/issues/136432

@zcallahan suggests we might be able to sidestep it by simply disabling CGO, which I think we could do in Formula/bbctl.rb by putting ENV["CGO_ENABLED"] = "0" at the top of our install function.