Add ChangeLog note about Binaryen optimizations

Author: dschuff

ChangeLog.md

@@ -29,6 +29,8 @@ See docs/process.md for more on how version tagging works.
 - The number of arguments passed to Embind function calls is now only verified
   with ASSERTIONS enabled. (#22591)
 - Optional arguments can now be omitted from Embind function calls. (#22591)
+- Recent changes to Binaryen included in this version significantly improve
+  the speed at which the post-link optimizations run for some large programs.
 
 3.1.67 - 09/17/24
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