[InstCombine] restrict no-wrap propagation for i1/i2 to avoid miscompiles

This transform was added with 68c197f0,
and the post-commit review noted the potential
for miscompiles at narrow bitwidths.

I'm not sure how to expose the i1 nuw bug because we
already simplify that, but other cases show that
there are missing transforms to add in follow-up
patches.