Document negative form of warning options enabled by default [PR90467].

Document negative form of warning options enabled by default [PR90467].

2020-02-26  Sandra Loosemore  <sandra@codesourcery.com>

	PR c++/90467

	gcc/
	* doc/invoke.texi (Option Summary): Re-alphabetize warnings in
	C++ Language Options, Warning Options, and Static Analyzer
	Options lists.  Document negative form of options enabled by
	default.  Move some things around to more accurately sort
	warnings by category.
	(C++ Dialect Options, Warning Options, Static Analyzer
	Options): Document negative form of options when enabled by
	default.  Move some things around to more accurately sort
	warnings by category.  Add some missing index entries.
	Light copy-editing.