Make lwp_info.arch_private handling shared

Make lwp_info.arch_private handling shared

This commit moves the code to handle lwp_info.arch_private for
Linux x86 into a new shared file, nat/x86-linux.c.

gdb/ChangeLog:

	* nat/x86-linux.h: New file.
	* nat/x86-linux.c: Likewise.
	* Makefile.in (HFILES_NO_SRCDIR): Add nat/x86-linux.h.
	(x86-linux.o): New rule.
	* config/i386/linux.mh (NATDEPFILES): Add x86-linux.o.
	* config/i386/linux64.mh (NATDEPFILES): Likewise.
	* nat/linux-nat.h (struct arch_lwp_info): New forward declaration.
	(lwp_set_arch_private_info): New declaration.
	(lwp_arch_private_info): Likewise.
	* linux-nat.c (lwp_set_arch_private_info): New function.
	(lwp_arch_private_info): Likewise.
	* x86-linux-nat.c: Include nat/x86-linux.h.
	(arch_lwp_info): Removed structure.
	(update_debug_registers_callback):
	Use lwp_set_debug_registers_changed.
	(x86_linux_prepare_to_resume): Use lwp_debug_registers_changed
	and lwp_set_debug_registers_changed.
	(x86_linux_new_thread): Use lwp_set_debug_registers_changed.

gdb/gdbserver/ChangeLog:

	* Makefile.in (x86-linux.o): New rule.
	* configure.srv: Add x86-linux.o to relevant targets.
	* linux-low.c (lwp_set_arch_private_info): New function.
	(lwp_arch_private_info): Likewise.
	* linux-x86-low.c: Include nat/x86-linux.h.
	(arch_lwp_info): Removed structure.
	(update_debug_registers_callback):
	Use lwp_set_debug_registers_changed.
	(x86_linux_prepare_to_resume): Use lwp_debug_registers_changed
	and lwp_set_debug_registers_changed.
	(x86_linux_new_thread): Use lwp_set_debug_registers_changed.