Now there's a single version of the main loop that runs once in normal
mode and repeatedly in AFL++ persistent mode. In persistent mode,
fmemopen() allows the loop to read the shared-memory buffer as though
it were a stdio stream. fmemopen() is POSIX-only, but so is AFL++.
Rather than a save file from standard input and then exiting, this reads
it from a shared memory buffer and then loops. This makes fuzzing
_much_ faster: one core on my laptop can now load about 30,000 save
files per second.