Recognize FreeBSD core dump note for x86 segment base registers.

Recognize FreeBSD core dump note for x86 segment base registers.

This core dump note contains the value of the base address of the %fs
and %gs segments for both i386 and amd64 core dumps.  It is primarily
useful in resolving the address of TLS variables in core dumps.

binutils/ChangeLog:

	* readelf.c (get_freebsd_elfcore_note_type): Handle
	NT_FREEBSD_X86_SEGBASES.

include/ChangeLog:

	* elf/common.h (NT_FREEBSD_X86_SEGBASES): Define.