Recognize the recently-added FreeBSD core dump note for LWP info.

This core dump note contains the same information returned by the
ptrace PT_LWPINFO operation for each LWP belonging to a process.

binutils/ChangeLog:

	* readelf.c (get_freebsd_elfcore_note_type): Handle
	NT_FREEBSD_PTLWPINFO.

include/ChangeLog:

	* elf/common.h (NT_FREEBSD_PTLWPINFO): Define.