explicit structure sharing in typed accessor function definitions

for bitwise-reproducible builds of src/compiler/info-vector.lisp
fix a code-walking-related nondeterminism

the assemble macro walks its body to collect labels, and carefully
manages the set of labels with set operations.  Sensible!  I hear
you cry: except that the sets of label names are then bound to label
objects in order, which if the set representations do not themselves
share an order leads to differences in machine code.  Fix this by
sorting appropriate lists, making sure to generate fresh list
structure where potentially necessary.