Fix sets for architectures with default integers smaller than 32 bits

[PMunch]

As discussed on IRC I recently discovered that sets didn't work properly on Arduino boards. Something as simple as this would fail:

var mySet: set[0..20]
mySet.incl 17
if not mySet.contains 17:
  # This branch would get executed, even though 17 is obviously meant to be in the set

The core of the issue turned out to be that AVR har 16-bit default integers, which means that checking for any number larger than 16 in a set small enough to be defined as a regular integer and not an array would fail. This is caused by a left shift on the default sized integer which would silently overflow and use an empty mask to check.