Currently we only make the base_architecture globally available, this
means we can tell if we have selected arc700/archs/etc but it's not
possible to tell if the user has selected a specific cpu variant, for
example nps400.

One problem this causes is, for example, in arc-c.def, if we want to add
an __NPS400__ define then we need a flag we can check to determine if
this is the right thing to do.

In this commit the arc_selected_cpu variable (previously local within
arc.c) has been made global.  Two other variables arc_base_cpu and
arc_selected_arch have been deleted, all of this information can be
found within (or through) arc_selected_cpu.

All uses of arc_base_cpu and arc_selected_arch have been updated.  This
commit does not introduce any new defines (like __NPS400__), this is
just a restructuring commit.

The declaration of arc_selected_cpu has moved into arc-arch.h, in
contrast to the declaration of arc_base_cpu which was previously in
arc.h.  This avoids a compilation issue when building libgcc, as the
structure and enums declared in arc-arch.h are not included for libgcc
then declaring an arc_selected_cpu (a struct type) in arc.h would result
in an unknown struct error.  We got away with this for arc_base_cpu as
that was an enum type.  The declaration of arc_selected_cpu in
arc.h could have been wrapped in a '#ifndef IN_LIBGCC2 ... #endif', but
it felt neater to simply move the declaration into arc-arch.h.

gcc/ChangeLog:

	* config/arc/arc-arch.h (arc_arch_t): Move unchanged to earlier in
	file.
	(arc_cpu_t): Change base_architecture field, arch, to a arc_arc_t
	pointer, arch_info.
	(arc_cpu_types): Fill the arch_info field with a pointer into the
	arc_arch_types table.
	(arc_selected_cpu): Declare.
	* config/arc/arc.c (arc_selected_cpu): Make global.
	(arc_selected_arch): Delete.
	(arc_base_cpu): Delete.
	(arc_override_options): Remove references to deleted variables,
	update access to arch information.
	(ARC_OPT): Update access to arch information.
	(ARC_OPTX): Likewise.
	* config/arc/arc.h (arc_base_cpu): Remove declaration.
	(TARGET_ARC600): Update access to arch information.
	(TARGET_ARC601): Likewise.
	(TARGET_ARC700): Likewise.
	(TARGET_EM): Likewise.
	(TARGET_HS): Likewise.
	* config/arc/driver-arc.c (arc_cpu_to_as): Update access to arch
	information.

From-SVN: r245293