Note newly enabled features in LLVM in ChangeLog

llvm/llvm-project#80923 enabled multivalue and
reference-types by default. Even though this is an LLVM change, given
that we release emsdk with all LLVM/Binaryen/Emscripten versions, it
could be worth mentioning in the ChangeLog.

ChangeLog.md

@@ -24,6 +24,9 @@ See docs/process.md for more on how version tagging works.
   of pthread builds so that is generated alongside the main JavaScript file.
   See #21701. ()
 - `-sASYNCIFY=2` is setting now deprecated, use `-sJSPI` instead.
+- LLVM now enables multivalue and reference-types features by default. Enabling
+  multivalue feature only enables the language feature and does not turn on the
+  multivalue ABI. (https://github.com/llvm/llvm-project/pull/80923)
 
 3.1.58 - 04/23/24
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