Introduce -fprofile-reproducibility and support it with TOP N.

Introduce -fprofile-reproducibility and support it with TOP N.

	PR ipa/92924
	* common.opt: Add -fprofile-reproducibility.
	* doc/invoke.texi: Document it.
	* value-prof.c (dump_histogram_value):
	Document and support behavior for counters[0]
	being a negative value.
	(get_nth_most_common_value): Handle negative
	counters[0] in respect to flag_profile_reproducible.
	PR ipa/92924
	* libgcov-merge.c (merge_topn_values_set): Record
	when a TOP N counter becomes invalid.  When merging
	remove a smallest value if the space is needed.