Blender Git Loki

Makesdna: Fix detecting 32 bit padding issues.

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