Define HAS_CPUID/HAS_I586/HAS_I686 from -march=

cpuid, i586 and i686 instructions are available if the processor
specified by -march= supports them.  We can use this information
to determine whether those instructions can be used safely.

	* sysdeps/x86/cpu-features.c (init_cpu_features): Check
	whether cpuid is available only if HAS_CPUID is 0.
	* sysdeps/x86/cpu-features.h (HAS_CPUID): New.
	(HAS_I586): Likewise.
	(HAS_I686): Likewise.