Add afl fuzzing helpers.

tools/afl/fuzz.sh

@@ -0,0 +1,36 @@
+set -eux
+
+NFUZZ=${NFUZZ:-1}
+children=""
+
+function finish {
+  for pid in $children
+  do
+    set +e
+    kill -s INT $pid
+  done
+  wait
+}
+trap finish EXIT
+
+test -e ./tools/afl/$1_testcases
+test -e ./tools/afl/$1_runner.janet
+
+echo "running fuzz master..."
+xterm -e \
+  "afl-fuzz -i ./tools/afl/$1_testcases -o ./fuzz_out/$1 -M Fuzz$1_0 -- ./build/janet ./tools/afl/$1_runner.janet @@" &
+children="$! $children"
+echo "waiting for afl to get started before starting secondary fuzzers"
+sleep 10
+
+NFUZZ=$((NFUZZ - 1))
+
+for N in $(seq $NFUZZ)
+do
+  xterm -e \
+    "afl-fuzz -i ./tools/afl/$1_testcases -o ./fuzz_out/$1 -S Fuzz$1_$N -- ./build/janet ./tools/afl/$1_runner.janet @@" &
+  children="$! $children"
+done
+
+echo "waiting for child terminals to exit."
+wait