libFuzzer arguments aren't passed to the underlying binary with -j

[TheBlueMatt]

eg if you are passing -detect_leaks=0: cargo fuzz run --features libfuzzer_fuzz full_stack_target -- -detect_leaks=0 works fine, cargo fuzz run --features libfuzzer_fuzz -j2 full_stack_target -- -detect_leaks=0 does not get the -detect_leaks argument passed through.