Fixup OPTION_SET_P usage in finish_options

When some code was moved from process_options to finish_options,
uses of OPTION_SET_P were not replaced with references to the
opts_set option set.  The following fixes this.

2022-05-03  Richard Biener  <rguenther@suse.de>

	* opts.cc: #undef OPTIONS_SET_P.
	(finish_options): Use opts_set instead of OPTIONS_SET_P.