Document option -fdump-ipa-clones

I have noticed that the option -fdump-ipa-clones is not documented
although there are users who depend on it.  This patch adds the
missing documentation along with the description of the information it
dumps and the format it uses.

I am never quite sure which of the texinfo mark-ups is the most
appropriate in which situation, I'll of course incorporate any
feedback on this as well as the general wording of the text.

After we settle on a version, I'd like to backport the documentation
also at least to GCC 15, 14 and 13.

Is it perhaps OK for master and the branches or what would better be
changed?

Thanks,

Martin

gcc/ChangeLog:

2025-04-23  Martin Jambor  <mjambor@suse.cz>

	* doc/invoke.texi (Developer Options): Document -fdump-ipa-clones.

(cherry picked from commit 6ecc2fee06bdd60da0e9b3fe6660b553dbdca3ca)