Add pointers mode to IEX tests

[rtadros125]

Currently, the IEX tests only leak string secrets. Add a 2nd mode to leak pointer secrets.

See #1236 and the work done by SRI-UCam on the CTSRD-CHERI:capability-leak-tests branch.

What needs to be done:

• [ ] Integrate into the clafer model, and thus the CWEs mapping to include both variants.
• [ ] Decide on how the secret will be stored (padding? a bit to convey local/global?)
• [ ] How control.c/h will change? How the variant choice will propagate to the control part?
• [ ] How this will affect the stores? Any more changes needed like Cheri, or will it be simpler? How will the variant choice propagate?
• [ ] Test on: FreeRTOS/FreeBSD/Debian and GCC/Clang (and verify the concept works as desired).