Changes

Generic hashing for the new closure representation (#9648, #9689)

This commit revises the generic hash functions to take advantage of
the new closure representation: code pointers are directly mixed
into the hash rather than having to be detected using Is_in_value_area.

Currently the new code for closures is activated only in no-naked-pointers
mode, even though it is sound in naked-pointers mode too.

Closes: #2168
 (commit: 0d1f7b2)