Add hardware watchpoint support for x86 GNU Hurd.

Add hardware watchpoint support for x86 GNU Hurd.

	gdb/
	* config/i386/i386gnu.mh (NATDEPFILES): Add x86-nat.o and
	x86-dregs.o.
	* gnu-nat.c (inf_threads): New function.
	* gnu-nat.h (inf_threads_ftype): New typedef.
	(inf_threads): New declaration.
	* i386gnu-nat.c: Include "x86-nat.h" and "inf-child.h".
	[i386_DEBUG_STATE] (i386_gnu_dr_get, i386_gnu_dr_set)
	(i386_gnu_dr_set_control_one, i386_gnu_dr_set_control)
	(i386_gnu_dr_set_addr_one, i386_gnu_dr_set_addr)
	(i386_gnu_dr_get_reg, i386_gnu_dr_get_addr, 386_gnu_dr_get_status)
	(i386_gnu_dr_get_control): New functions.
	(reg_addr): New structure.
	(_initialize_i386gnu_nat) [i386_DEBUG_STATE]: Initialize hardware
	i386 debugging register hooks.
	* NEWS: Mention this.