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
Differential Revision: https://developer.blender.org/D12188
Reviewed by: sergey, campbellbarton
45d100208e