Port AFL stuff from zcash upstream

zcutil/afl/afl-get.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+# Obtains and builds a copy of AFL from source.
+#   ./zcutil/afl/afl-get.sh <directory to build and install AFL in>
+
+set -eu -o pipefail
+
+mkdir -p "$1"
+cd "$1"
+
+if [ ! -z "$(ls -A .)" ]; then
+    echo "$1 is not empty. This script will only attempt to build AFL in an empty directory."
+    exit 1
+fi
+
+# Get the AFL source
+rm -f afl-latest.tgz
+wget http://lcamtuf.coredump.cx/afl/releases/afl-latest.tgz
+sha256sum afl-latest.tgz | grep '43614b4b91c014d39ef086c5cc84ff5f068010c264c2c05bf199df60898ce045'
+if [ "$?" != "0" ]
+then
+    echo "Wrong SHA256 hash for afl"
+    exit
+fi
+tar xvf afl-latest.tgz
+mv afl-*/* .
+
+# Build AFL
+make
+
+echo "You can now build zcashd with AFL instrumentation as follows:"
+echo "$ make clean # if you've already built zcashd without AFL instrumentation"
+echo "$ ./zcutil/afl/afl-build.sh '$(pwd)' <fuzz case> -j\$(nproc)"
+echo "...where <fuzz case> is the name of a directory in src/fuzzing."