[clang][doc] Add release note for changes to -fveclib={ArmPL,SLEEF} (llvm#113673)

Changed in llvm#112580.

Author: MacDue

clang/docs/ReleaseNotes.rst

@@ -302,6 +302,11 @@ Modified Compiler Flags
   the ``promoted`` algorithm for complex division when possible rather than the
   less basic (limited range) algorithm.
 
+- The ``-fveclib`` option has been updated to enable ``-fno-math-errno`` for
+  ``-fveclib=ArmPL`` and ``-fveclib=SLEEF``. This gives Clang more opportunities
+  to utilize these vector libraries. The behavior for all other vector function
+  libraries remains unchanged.
+
 Removed Compiler Flags
 -------------------------