Generate Errno and Pod::Functions with deterministic order.

Generate Errno and Pod::Functions with deterministic order.

Previously the order of duplicate names in Errno was determined by hash
iteration order, as was the order of the list of types for built-ins in
Pod::Functions. With hash randomisation this meant that the generated file
could differ between builds, which isn't ideal if the input is the same.

(Spotted as a side effect of running a diff on two installation trees.)