demo: use --set-section-alignment when using objcopy

demo: use --set-section-alignment when using objcopy

If we don't set the alignment then there is a chance that it ends up
commonly on a 4-byte boundary and GResources will have to malloc/memcpy
the static data.

With --set-section-alignment (which takes a byte offset not ^2) available
in objcopy >= 2.33 we ensure that expectation is met.