services: nscd: Create /etc/resolv.conf if it does not exist.

* gnu/services/base.scm (nscd-activation): Create /etc/resolv.conf if it
does not exist yet.

gnu/services/base.scm

@@ -1149,7 +1149,14 @@ (define nscd-activation
   #~(begin
       (use-modules (guix build utils))
       (mkdir-p "/var/run/nscd")
-      (mkdir-p "/var/db/nscd")))                  ;for the persistent cache
+      (mkdir-p "/var/db/nscd")                    ;for the persistent cache
+
+      ;; In libc 2.25 nscd uses inotify to watch /etc/resolv.conf, but only if
+      ;; that file exists when it is started.  Thus create it here.
+      (unless (file-exists? "/etc/resolv.conf")
+        (call-with-output-file "/etc/resolv.conf"
+          (lambda (port)
+            (display "# This is a placeholder.\n" port))))))
 
 (define nscd-service-type
   (service-type (name 'nscd)