Require opd_mode_1_7i77_struct to be word-aligned

This fixes a diagnostic seen on Ubuntu 10.04 building the examples:

converting a packed 'opd_mode_1_7i77_t' {aka 'struct
opd_mode_1_7i77_struct'} pointer (alignment 1) to a 'u32' {aka 'unsigned int'}
pointer (alignment 4) may result in an unaligned pointer value
[-Werror=address-of-packed-member]