Persistent mode is always enabled

[boryspoplawski]

After commit hfuzz-cc: ensure libhfuzz is linked to executables (904b577) all executables build with hfuzz-clang are forced into persistent mode.

Repro:

$ cat test.c 
int main(void) {
    return 0;
}
$ ~/honggfuzz/hfuzz_cc/hfuzz-clang -o test test.c
$ ~/honggfuzz/honggfuzz -i inputs/ -z -s -- ./test

Runs in persistent mode and there seems to be no way of disabling it.

Adding a command line option to disable the persistent mode would be one way of fixing it, though I believe the auto-detection is a bit over aggresive :)