Share i386-linux target description between GDB and GDBserver

Share i386-linux target description between GDB and GDBserver

The code on creating i386-linux target descriptions are quite similar
between GDB and GDBserver, so this patch moves them into a shared file
arch/i386.c.  I didn't name it as i386-linux.c, because I want to reuse it
to create other i386 non-linux target descriptions later.

gdb:

2017-09-05  Yao Qi  <yao.qi@linaro.org>

	* Makefile.in (ALL_TARGET_OBS): Add i386.o.
	(SFILES): Add arch/i386.c.
	(HFILES_NO_SRCDIR): Add arch/i386.h.
	* arch/i386.c: New file.
	* arch/i386.h: New file.
	* arch/tdesc.h (allocate_target_description): Declare.
	(set_tdesc_architecture): Declare.
	(set_tdesc_osabi): Declare.
	* configure.tgt (i[34567]86-*-linux*): Add i386.o.
	* i386-linux-tdep.c: Don't include ../features/i386/32bit-XXX.c.
	include arch/i386.h.
	(i386_linux_read_description): Remove code and call
	i386_create_target_description.
	(set_tdesc_architecture): New function.
	(set_tdesc_osabi): New function.
	* target-descriptions.h (allocate_target_description): Remove.

gdb/gdbserver:

2017-09-05  Yao Qi  <yao.qi@linaro.org>

	* Makefile.in (arch-i386.o): New rule.
	* configure.srv (i[34567]86-*-linux*): Add arch-i386.o.
	(x86_64-*-linux*): Likewise.
	* linux-x86-tdesc.c: Don't include ../features/i386/32bit-XXX.c,
	include arch/i386.h.
	(i386_linux_read_description): Remove code and call
	i386_create_target_description.
	* tdesc.c (allocate_target_description): New function.
	* tdesc.h (set_tdesc_architecture): Remove declaration.
	(set_tdesc_osabi): Likewise.