will_set_contents_of_parameter() should save the data

[thoni56]

I often get bit by the issue that the data pointed to when calling will_set_contents_of_parameter(<parameter>, pointer_to_data, length) has to be retained until the actual call to the mock. This is documented but it would be much better if this wasn't an issue at all.

The expectation is probably that once the expect() has run you can forget about it, which is not the case.

I think it would be possible to memcpy() the data to an allocated area held by the expectation/constraint. This way it is saved from destruction until it is needed, used and discarded.