Removing native_name reference from constant_body.

For now, this reference (renamed to link_info) has been moved to the
environment (for constants and inductive types). But this is only a first step
towards making the native compiler more functional.
Revert "Partial revert of r16711"

The sharing introduced by this commit is now correct, since a reference used by
the native compiler has been removed from constant_body.

This reverts commit 413f5fcd4bf581ff3ea4694c193d637589c7d54f.