Comment 1 for bug 313226

The attached patch doesn't quite get rid of constraint propagation, but reduces it.

(setf sb-c::*constraint-propagation-rounds* 0)

makes things build a fair bit faster (50% reduction in compile-time eg. for DEFINE-EXTERNAL-FORMAT :UTF-8) -- but breaks some things.

(setf sb-c::*constraint-propagation-rounds* 1)

should always work, but improves compiler performance by only about 6% on average: for some cases likely by much more. No measurements on the effect of compiled code yet.