All instructions support fixed as per review comments

For each instruction, first build the klee expression and then
assert on its UB. In this, you will find a change in addInstCondition()
function. The reason to modify its rturn type from void to ref<Expr> is
it accepts a boolean expr as an argument and adding function calls, like:
addInstCondition(addnuwUB(ref<Expr> E, ...)) will not work because of type mismatch
as here the expected type must be Bool Expr but it is actually ref<Expr>

sdiv is also fixed in this commit.