Changes

extern.c: refactor the code using auxiliary functions

This makes the core function `extern_rec` easier to read, and will
avoid code duplication in later changes.
 (commit: 21ce6b0)

extern.c: use new closure representation to marshal closures

We know where the code pointers, closure info words and infix headers are,
and can output them directly.

Currently activated in no-naked-pointers mode only, but would work in
the other mode as well.
 (commit: c184094)

Changes entry for #9649
 (commit: 919803e)