cs: module in some error messages only when enabled

Check `(error-print-source-location)` before adding a module name in
an error message about use/set before definition.

racket/src/cs/linklet.sls

@@ -88,6 +88,7 @@
                 find-system-path
                 build-path
                 format
+                error-print-source-location
                 ;; Used by cross-compiler:
                 get-original-error-port
                 subprocess
@@ -844,6 +845,8 @@
                            "importing instance" (unquoted-printing-string (format "~a" (instance-name target-inst)))))
 
   (define (identify-module var)
+    (cond
+     [(error-print-source-location)
       (let ([i (car (variable-inst-box var))])
         (cond
          [(eq? i #!bwp)
@@ -851,7 +854,8 @@
          [(instance-name i)
           => (lambda (name)
                (#%format "\n  module: ~a" name))]
-       [else ""])))
+         [else ""]))]
+     [else ""]))
 
   (define (raise-undefined var set?)
     (raise