Support several new ELF auxiliary vector types on FreeBSD.

Support several new ELF auxiliary vector types on FreeBSD.

FreeBSD's kernel recently added several ELF auxiliary vector entries
to describe the arguments passed to new executable images during
exec().  The AT_FREEBSD_ARGC and AT_FREEBSD_ARGV entries give the
length and address of the process argument array.  AT_FREEBSD_ENVC and
AT_FREEBSD_ENVV entries give the length and address of the initial
process environment.  AT_FREEBSD_PS_STRINGS gives the address of the
'struct ps_strings' object.

include/ChangeLog:

	* elf/common.h (AT_FREEBSD_ARGC, AT_FREEBSD_ARGV, AT_FREEBSD_ENVC)
	(AT_FREEBSD_ENVV, AT_FREEBSD_PS_STRINGS): Define.

gdb/ChangeLog:

	* fbsd-tdep.c (fbsd_print_auxv_entry): Handle AT_FREEBSD_ARGC,
	AT_FREEBSD_ARGV, AT_FREEBSD_ENVC, AT_FREEBSD_ENVV,
	AT_FREEBSD_PS_STRINGS.