fix links on clang 18.1.0rc release page (#82739)

Looking at the [release
notes](https://prereleases.llvm.org/18.1.0/rc3/tools/clang/docs/ReleaseNotes.html

)
for clang 18.1.0rc, there's some broken links, and many issue numbers
mis-formatted with an extra colon. Aside from being used inconsistently
(with/without colon), I think it should be uncontroversial that `See
(#62707).` is better than `See (#62707:).`

CC @tstellar @AaronBallman

Co-authored-by: Aaron Ballman <aaron@aaronballman.com>