syscalls: Define AT_SYMLINK_NOFOLLOW et al.

* guix/build/syscalls.scm (AT_FDCWD, AT_SYMLINK_NOFOLLOW, AT_REMOVEDIR)
(AT_SYMLINK_FOLLOW, AT_NO_AUTOMOUNT, AT_EMPTY_PATH): New variables.
* tests/syscalls.scm ("utime with AT_SYMLINK_NOFOLLOW"): New test.

guix/build/syscalls.scm

@@ -46,6 +46,14 @@ (define-module (guix build syscalls)
             MNT_DETACH
             MNT_EXPIRE
             UMOUNT_NOFOLLOW
+
+            AT_FDCWD
+            AT_SYMLINK_NOFOLLOW
+            AT_REMOVEDIR
+            AT_SYMLINK_FOLLOW
+            AT_NO_AUTOMOUNT
+            AT_EMPTY_PATH
+
             restart-on-EINTR
             mount-points
             swapon
@@ -667,6 +675,15 @@ (define (free-disk-space file)
     (* (file-system-block-size fs)
        (file-system-blocks-available fs))))
 
+;; Flags for the *at command, notably the 'utime' procedure of libguile.
+;; From <fcntl.h>.
+(define AT_FDCWD             -100)
+(define AT_SYMLINK_NOFOLLOW #x100)
+(define AT_REMOVEDIR        #x200)
+(define AT_SYMLINK_FOLLOW   #x400)
+(define AT_NO_AUTOMOUNT     #x800)
+(define AT_EMPTY_PATH       #x1000)
+
 
 ;;;
 ;;; Containers.

tests/syscalls.scm

@@ -60,6 +60,19 @@ (define temp-file
   (any (cute member <> (mount-points))
        '("/" "/proc" "/sys" "/dev")))
 
+(false-if-exception (delete-file temp-file))
+(test-equal "utime with AT_SYMLINK_NOFOLLOW"
+  '(0 0)
+  (begin
+    ;; Test libguile's utime with AT_SYMLINK_NOFOLLOW, which libguile does not
+    ;; define as of Guile 2.2.4.
+    (symlink "/nowhere" temp-file)
+    (utime temp-file 0 0 0 0 AT_SYMLINK_NOFOLLOW)
+    (let ((st (lstat temp-file)))
+      (delete-file temp-file)
+      ;; Note: 'utimensat' does not change 'ctime'.
+      (list (stat:mtime st) (stat:atime st)))))
+
 (test-assert "swapon, ENOENT/EPERM"
   (catch 'system-error
     (lambda ()