Feature: consider register with controllable content of pointer as gadgets' constraint about one_gadget

[david942j]

Currently constraints of all one-gadgets are some value(s) to be zero (NULL).
Maybe we should add another option to find gadgets that constraint is register to be a controllable string?

For example, if rdi is a controllable string then we can use system as 'one-gadget'.
And in your case, it works if r12 is a command string.

Maybe add an option --all then one_gadget <file> --all will show this kind of gadgets.

I think separate the null-condition and string-condition cases can prevent confusing users.