fix copy-file' reporting of exn:fail:filesystem:exists?'

Fixes re-report for PR 12074

collects/tests/racket/path.rktl

@@ -129,6 +129,8 @@
 (test #f copy-file/tf "tmp5" "down")
 (test #f copy-file/tf "tmp5" (build-path deepdir "moredeep" "tmp5y"))
 (test (file-size "tmp5") file-size "tmp5y")
+(err/rt-test (copy-file "tmp5" "tmp5y") exn:fail:filesystem:exists?)
+(err/rt-test (copy-file "no-such-tmp5" "tmp5y") (lambda (x) (not (exn:fail:filesystem:exists? x))))
 (delete-file "tmp5y")
 
 (test #t rename-file-or-directory/tf "tmp5" "tmp5x")

src/racket/src/file.c

@@ -3908,6 +3908,7 @@ static Scheme_Object *copy_file(int argc, Scheme_Object **argv)
     if (!out) {
       scheme_close_input_port(in);
       has_err_val = !!err_val;
+      pre_exists = (err_val == EEXIST);
       goto failed;
     }