config.gcc: Revamp target_cpu_default2 to strings; support new x86 variants.

config.gcc: Revamp target_cpu_default2 to strings; support new x86 variants.

	* config.gcc: Revamp target_cpu_default2 to strings;
	support new x86 variants.
	* i386.c (override_options): Default x86_cpu_string and x86_arch_string
	properly; set prefetch_sse.
	* i386.h (x86_prefetch_sse): Declare.
	(TARGET_PREFETCH_SSE): New.
	(CPP_CPU_DEFAULT_SPEC): Define according to the new macros.
	(TARGET_CPU_DEFAULT_*): New.
	* config/i386/i386.h (struct processor_costs): Add new members
	  prefetch_block and simultaneous_prefetches.
	  (PREFETCH_BLOCK, SIMULTANEOUS_PREFETCHES): New.
	* config/i386/i386.c (processor_costs structs): Add values for
	  prefetch_block and simultaneous_prefetches.
	* config/i386/i386.md (unspec values): Remove values for prefetch
	  operations, which now use the PREFETCH rtx code.
	  (prefetch_sse, prefetch_3dnow, prefetchw): Combine to use new
	  unified prefetch support.

From-SVN: r48006