makesdna fails to detect issues in 32 bit code that can
only be resolved by adding a padding pointer.

We never noticed since we ourselves no longer build for
32 bit, but debian's 32 bit builds got bitten by this

A rather extensive explanation on why this is alignment
requirement is there can be found in this comment:

https://developer.blender.org/D9389#233034

I have to admit, I do not enjoy working on makesdna and I'm
honestly terrified I broke it, review this very very critically

This is currently throwing out *LOTS* of errors that are
false positives (ie ModifierData need a padding field,
but it flags any structs that have ModifierData in it
as well) then again, that's just what makesdna seems to do
whenever it gets unhappy, so no change there.

D9389 needs to land before this can land.