ftw: Fix getuid-or-false, getgid-or-false macros.

Both macros were missing a quote for the procedure call, causing the
actual return value to be compiled into the ftw.go, instead of the
procedure call.  Snippet from disassembly of ftw.go does confirm that:

  55    (make-immediate 2 3990)         ;; 997                at ice-9/ftw.scm:319:46
  56    (make-long-immediate 1 120002)  ;; 30000              at ice-9/ftw.scm:320:46

That effectively prevented ftw from entering directories without access
for others.  Simple reproduction:

    scheme@(guile-user)> ,use (ice-9 ftw)
    scheme@(guile-user)> (mkdir "/tmp/xxxx")
    scheme@(guile-user)> (chmod "/tmp/xxxx" #o0700)
    scheme@(guile-user)> (ftw "/tmp/xxxx" (lambda (_ __ f) (pk f) #t))

    ;;; (directory-not-readable)
    $1 = #t
    scheme@(guile-user)> (system "ls -al /tmp/xxxx")
    total 0
    drwx------ 1 wolf wolf   0 Oct 11 22:54 .
    drwxrwxrwt 1 root root 888 Oct 11 22:54 ..
    $2 = 0

The fix is to quote the procedure call, leading to the intended
behavior.

Fixes <https://bugs.gnu.org/55344>.

* module/ice-9/ftw.scm (getuid-or-false): Quote the (getuid).
(getgid-or-false): Quote the (getgid).
* NEWS: Update.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

NEWS

@@ -41,6 +41,8 @@ the compiler reports it as "possibly unused".
    (<https://bugs.gnu.org/55356>)
 ** 'read-u8' in (scheme base) now defaults to (current-input-port)
    (<https://bugs.gnu.org/62690>)
+** 'ftw' now correctly deals with directory permissions
+   (<https://bugs.gnu.org/55344>)
 ** Hashing of UTF-8 symbols with non-ASCII characters avoids corruption
    (<https://bugs.gnu.org/56413>)
 

module/ice-9/ftw.scm

@@ -201,12 +201,12 @@
 
 (define-macro (getuid-or-false)
   (if (defined? 'getuid)
-      (getuid)
+      '(getuid)
       #f))
 
 (define-macro (getgid-or-false)
   (if (defined? 'getgid)
-      (getgid)
+      '(getgid)
       #f))
 
 (define (directory-files dir)