cppdiropts.texi, [...]: New files, split from...

2016-12-27  Sandra Loosemore  <sandra@codesourcery.com>

	gcc/
	* doc/cppdiropts.texi, doc/cppwarnopts.texi:  New files, split from...
	* doc/cppopts.texi: .... here.
	* doc/cpp.texi (Invocation): Adjust includes.
	* doc/invoke.texi (Option Summary): Add missing preprocesor-related
	options.  Adjust sorting and formatting.
	(Warning Options): Include cppwarnopts.texi.
	(Preprocessor Options): Add pointers and list the specific 
	preprocessor options from cppopts.texi first instead of last.
	(Directory Options): Move/merge documentation of -I, -iquote, and
	-I- to cppdiropts.texi.  Include that file here.

From-SVN: r243954