fuzz: Change the save directory to fuzz/runs rather than target

The target directory is cached in CI but there is no reason to cache
fuzzing results.

Author: tgross35

.gitignore

@@ -7,3 +7,4 @@ rustc-ice*
 # Fuzzing data/state.
 /fuzz/in*
 /fuzz/out*
+/fuzz/runs

README.md

@@ -99,13 +99,13 @@ mkdir fuzz/in-foo && echo > fuzz/in-foo/empty
 
 # Start the fuzzing run `foo`, which should bring up the AFL++ progress TUI
 # (see also `cargo run -p rustc_apfloat-fuzz` for extra flags available).
-cargo afl fuzz -i fuzz/in-foo -o fuzz/out-foo target/release/rustc_apfloat-fuzz
+cargo afl fuzz -i fuzz/run/in-foo -o fuzz/run/out-foo target/release/rustc_apfloat-fuzz
 ```
 
 To visualize the fuzzing testcases, you can use the `decode` subcommand:
 
 ```sh
-cargo run -p rustc_apfloat-fuzz decode fuzz/out-foo/default/crashes/*
+cargo run -p rustc_apfloat-fuzz decode fuzz/run/out-foo/default/crashes/*
 ```
 
 Note that `cargo run` and `cargo afl build` conflict, so if running the fuzzer

etc/fuzz-parallel.sh

@@ -9,8 +9,8 @@ set -euxo pipefail
 # Detect cores
 all_cores="$(nproc)"
 used_cores="$((all_cores - 2))"
-in_dir="target/fuzz-in"
-sync_dir="target/fuzz-out"
+in_dir="fuzz/runs/fuzz-in"
+sync_dir="fuzz/runs/fuzz-out"
 tmux_window=afl
 
 if [[ "$used_cores" -lt 2 ]]; then