PR28422, build_id use-after-free

This fixes a bug in commit 5d9bbb73c1df.  All fields preserved from a
bfd in struct bfd_preserve need to be cleared in bfd_reinit.

	PR 28422
	* format.c (bfd_reinit): Clear build_id.

(cherry picked from commit 6d661cdc5be46e890ed9255e749806f46a88e26c)