tools/insn-fuzz: Avoid making use of static data

tools/insn-fuzz: Avoid making use of static data

AFL has a measure of stability, where it passes the same corpus into the
fuzzing harness and observes whether the execution path changes from before.
Any instability in the fuzzing harness reduces its effectiveness, as an
observed crash may not reliably be caused by the original corpus.

In preparation to fix a stability bug, introduce struct fuzz_state, allocated
on the stack and passed around via struct x86_emulate_ctxt's data parameter.
Propagate ctxt into the helpers such as maybe_fail(), so the state can be
retrieved.

Move the previously-static data_{index,num} into struct fuzz_state.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>