Update Language Extensions docs for backporting

AaronBallman · AaronBallman · commit 07207716fe04 · 2025-10-09T12:15:37.000-04:00
diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
@@ -1823,6 +1823,7 @@ Octal literals prefixed with ``0o`` or ``0O``                                  C
 ``_Countof`` (N3369, N3469)                                                    C2y           C89
 ``_Generic`` with a type operand (N3260)                                       C2y           C89, C++
 ``++``/``--`` on ``_Complex`` value (N3259)                                    C2y           C89, C++
+``__COUNTER__`` (N3457)                                                        C2y           C89, C++
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 Builtin type aliases
