Update x86 --with-arch/--with-cpu= configure handling

	PR bootstrap/59580
	PR bootstrap/59583
	* config.gcc (x86_archs): New variable.
	(x86_64_archs): Likewise.
	(x86_cpus): Likewise.
	Use $x86_archs, $x86_64_archs and $x86_cpus to check valid
	--with-arch/--with-cpu= options.
	Support --with-arch=/--with-cpu={nehalem,westmere,
	sandybridge,ivybridge,haswell,broadwell,bonnell,silvermont}.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@206756 138bc75d-0d04-0410-961f-82ee72b054a4