set_ios builtin allows you to set a specific IO space as the
new current IO space. It has the following prototype:
fun set_ios = (int<32> ios) int<32>
where ios is the IO space that will become the current IO
space. If the IO space specified to
set_ios doesn’t exist,
E_no_ios will be raised.
set_ios always returns
1. This is to ease its
usage in struct fields constraint expressions.