c.opt: Document Uncodumented; use it.

c.opt: Document Uncodumented; use it.

	* c.opt: Document Uncodumented; use it.  Document ObjC options.
	* opts.c (print_filtered_help): Skip undocumented switches.
	* opts.h (CL_UNDOCUMENTED): New.
	* opts.sh: Handle Undocumented.
	* toplev.c (documented_lang_options): Prevent its becoming empty.
f:
	* lang-options.h: Remove.
	* lang.opt: Document most options.
objc:
	* lang-options.h: Remove.

From-SVN: r69494