services: shepherd: Compile service files.

This reduces resident memory for PID 1 from 29.8MiB to 28.7MiB right
after boot on a bare-bones system (x86_64-linux).

* gnu/services/shepherd.scm (scm->go): New procedure.
(shepherd-configuration-file)[config]: Call it and use 'load-compiled'
instead of 'primitive-load'.

gnu/services/shepherd.scm

@@ -255,6 +255,22 @@ stored."
                                    #~(#$name #$doc #$proc)))
                                 (shepherd-service-actions service))))))))
 
+(define (scm->go file)
+  "Compile FILE, which contains code to be loaded by shepherd's config file,
+and return the resulting '.go' file."
+  (with-extensions (list shepherd)
+    (computed-file (string-append (basename (scheme-file-name file) ".scm")
+                                  ".go")
+                   #~(begin
+                       (use-modules (system base compile))
+
+                       ;; Do the same as the Shepherd's 'load-in-user-module'.
+                       (let ((env (make-fresh-user-module)))
+                         (module-use! env (resolve-interface '(oop goops)))
+                         (module-use! env (resolve-interface '(shepherd service)))
+                         (compile-file #$file #:output-file #$output
+                                       #:env env))))))
+
 (define (shepherd-configuration-file services)
   "Return the shepherd configuration file for SERVICES."
   (assert-valid-graph services)
@@ -269,7 +285,8 @@ stored."
           ;; than a kernel panic.
           (call-with-error-handling
             (lambda ()
-              (apply register-services (map primitive-load '#$files))
+              (apply register-services
+                     (map load-compiled '#$(map scm->go files)))))
 
           ;; guix-daemon 0.6 aborts if 'PATH' is undefined, so work around
           ;; it.
@@ -298,7 +315,7 @@ stored."
           ;; PID 1 to read from stdin (the console), which users may not
           ;; have access to (see <https://bugs.gnu.org/23697>).
           (redirect-port (open-input-file "/dev/null")
-                             (current-input-port))))))
+                         (current-input-port))))
 
     (scheme-file "shepherd.conf" config)))