config.gcc: Reorganize --with-cpu logic.

	* config.gcc: Reorganize --with-cpu logic.  Set
	configure_default_options according to the default CPU, --with-cpu,
	--with-arch, --with-tune, --with-schedule, --with-abi, and
	--with-float.  Check for legal values of various options.
	* configure.in: Define configure_default_options in configargs.h.
	* configure: Regenerated.
	* config/mips/mips.h (TARGET_DEFAULT_ARCH_P)
	(TARGET_DEFAULT_FLOAT_P): New macros.
	* gcc.c (do_option_spec): New function.
	(struct default_spec, option_default_specs): New.
	(main): Call do_option_spec.
	* config/alpha/alpha.h, config/arm/arm.h, config/i386/i386.h,
	config/mips/mips.h, config/pa/pa.h, config/rs6000/rs6000.h,
	config/sparc/sparc.h (OPTION_DEFAULT_SPECS): Define.

	* doc/install.texi: Update --with-cpu documentation.  Mention
	--with-arch, --with-schedule, --with-tune, --with-abi, and
	--with-float.
	* doc/tm.texi (Driver): Document OPTION_DEFAULT_SPECS.

From-SVN: r67457