invoke.texi (Submodel Options): Rename section to "Machine-Dependent Options" to better reflect its content.

2016-01-13  Sandra Loosemore <sandra@codesourcery.com>

	gcc/
	* doc/invoke.texi (Submodel Options): Rename section to
	"Machine-Dependent Options" to better reflect its content.
	Rewrite introductory text to remove archaic CPU names.
	Update references.

From-SVN: r232355