* target.h (struct target_ops): New member to_thread_architecture.

	* target.h (struct target_ops): New member to_thread_architecture.
	(target_thread_architecture): New macro.
	* target.c (update_current_target): Inherit to_thread_architecture.
	(default_thread_architecture): New function.
	(debug_to_thread_architecture): New function.
	(setup_target_debug): Handle to_thread_architecture.

	* regcache.h (get_thread_arch_regcache): New.
	* regcache.c (struct regcache_list): New data type.
	(current_regcache): Hold regcache list instead of single regcache.
	(current_thread_ptid, current_thread_arch): New static variables.
	(get_thread_arch_regcache): New function.
	(get_thread_regcache): Use it.  Call target_thread_architecture.
	(regcache_thread_ptid_changed): Update to current_regcache changes.
	(registers_changed): Likewise.  Reset current_thread_arch and
	current_thread_ptid.

	* remote.c (remote_wait): Access target registers in target_gdbarch.
	* linux-nat.c (linux_nat_do_thread_registers): Likewise.
	* proc-service.c (ps_lgetregs, ps_lsetregs): Likewise.
	(ps_lgetfpregs, ps_lsetfpregs): Likewise.
	* sol-thread.c (ps_lgetregs, ps_lsetregs): Likewise.
	(ps_lgetfpregs, ps_lsetfpregs): Likewise.
	* solib-svr4.c (enable_break): Likewise.
	(svr4_relocate_main_executable): Likewise.