[Clang] [Docs] Add release notes for #143514 and #143520 (#147562)

I forgot to include a release note in #143520, and it also ocurred to me
that while #143514 is technically a bugfix in LLVM/Support, I think we
should have one for it as well.

Author: Sirraide

clang/docs/ReleaseNotes.rst

@@ -678,6 +678,12 @@ Improvements to Clang's diagnostics
 - Clang now accepts ``@tparam`` comments on variable template partial
   specializations. (#GH144775)
 
+- Fixed a bug that caused diagnostic line wrapping to not function correctly on
+  some systems. (#GH139499)
+
+- Clang now tries to avoid printing file paths that contain ``..``, instead preferring
+  the canonical file path if it ends up being shorter.
+
 Improvements to Clang's time-trace
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