Add main for fuzzer
Add main for fuzzer

Add simple main for fuzzing. This would make it easier to optimize some
processing for fuzzing and integrate with another fuzzer.
There are several duplicated lines in the original main function. I'll
plan to unify them later.

iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace