fix(3rd-party): fix mgen, ahp-xc and pentax errors on fedora.

[TallFurryMan]

fix(indi-mgen): work around C++14 out-of-bounds warnings.

This is a tentative PR to fix out-of-bounds warnings emitted by C++14 when building indi-mgen.

The implementation restricts the set of function candidates the compiler selects from when using an initialiser list on IOBuffer: IOBuffer{opcode,literal,literal...}, and makes sure to allocate space before copying the list data.

fix(indi-ahp-xc): silence warnings by allocating placeholders with their real size.

@iliaplatone I considered that placeholders with their real sizes instead of 1 byte everywhere wasn't that problematic. Feel free to comment.

fix(indi-pentax): fix calloc argument order.

calloc(sizeof,sizeof) expects the number of items as first argument, and the size of each as second.

[TallFurryMan]

Possibly the change in indi-mgen is not minimal. It builds without warnings in my local ghcr.io/indilib/fedora, so I suppose the idea may be used elsewhere in the codebase.

[TallFurryMan]

The fedora build fails because of other drivers, at least one for the same reason as this PR. I may have a look later this week-end.