Each of these examples needs a version that matches the version
of bftrace.

Refer to https://github.com/bpftrace/bpftrace/tree/master/tools#versioned-tools
for the supported list of bpftrace versions, and from there links to
the *.bt files we need.

To download the files for a particular version that we don't already
have, run

    ./Download <version>
