Eval macro arg just once

* lisp/emacs-lisp/cl-macs.el (cl--push-clause-loop-body):
Use `macroexp-let2' (Bug#39428).

Author: calancha

lisp/emacs-lisp/cl-macs.el

@@ -1037,9 +1037,10 @@ For more details, see Info node `(cl)Loop Facility'.
 
 (defmacro cl--push-clause-loop-body (clause)
   "Apply CLAUSE to both `cl--loop-conditions' and `cl--loop-body'."
-  `(progn
-     (push ,clause cl--loop-conditions)
-     (push ,clause cl--loop-body)))
+  (macroexp-let2 nil sym clause
+    `(progn
+       (push ,sym cl--loop-conditions)
+       (push ,sym cl--loop-body))))
 
 ;; Below is a complete spec for cl-loop, in several parts that correspond
 ;; to the syntax given in CLtL2.  The specs do more than specify where