re PR middle-end/37805 (gcc --help=separate)

re PR middle-end/37805 (gcc --help=separate)

gcc/
	PR middle-end/37805
	* opts.c (print_specific_help): In addition to `undocumented',
	accept `separate' and `joined' flags if passed alone.  Describe
	output by the first matched one of those.
	(common_handle_option): Skip over empty strings.
	* gcc.c (display_help): Fix help string for `--help='.
	* doc/invoke.texi (Option Summary, Overall Options): With
	`--help=', classes and qualifiers can both be repeated, but
	only the latter can be negated.  One should not pass only
	negated qualifiers.  Fix markup and examples.

From-SVN: r144921