CMake: Add ENABLE_FUZZING and "afl" target

fuzzing/afl.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+mkdir -p afl-build || exit 1
+cd afl-build || exit 1
+#cleanup
+rm -r -- *
+
+CC=afl-gcc cmake ../.. -DENABLE_FUZZING=On -DENABLE_SANITIZERS=On -DBUILD_SHARED_LIBS=Off
+make afl