Add the latest change to CHANGELOG

src/CHANGELOG

@@ -21,6 +21,15 @@ ECL 10.4.2:
 
  - ECL's compiler now understands the unboxed type :long-long.
 
+ - A new special form, EXT:WITH-BACKEND allows us to select the code depending
+   on whether it is going to be processed by the interpreter or by the C
+   compiler.
+      (defun example ()
+        (ext:with-backend (:bytecodes) (print 3))
+        (ext:with-backend (:c/c++) (print 2)))
+   The two currently available backends are :bytecodes and :c/c++. Note that
+   when the backend does not match the value, the form is replaced with (VALUES).
+
 
 ECL 10.4.1:
 ===========