Properly use opts in finish_options

Properly use opts in finish_options

When code was moved from process_options to finish_options it
was not properly adjusted to look at and alter the opts set
passed to the function but continued to modify the global options
set.  The following rectifies this and makes sure the same
mistake isn't repeated by poisoning global_options{,_set}.

2022-05-10  Richard Biener  <rguenther@suse.de>

	* flags.h (dwarf_debuginfo_p): Add opts argument, guard
	API with !GENERATOR_FILE.
	* opts.cc (global_options): Poison.
	(global_options_set): Likewise.
	(finish_options): Refer to options via opts.