build: Improve Guile 2.2 compatibility.

* build-aux/compile-all.scm (compile-file*): Ensure loading of
  compilation related modules before going parallel.
* guix/build/pull.scm (build-guix): Ditto.

build-aux/compile-all.scm

@@ -81,6 +81,9 @@
    (let ((files (filter file-needs-compilation? files)))
      (for-each load-module-file files)
      (let ((mutex (make-mutex)))
+       ;; Make sure compilation related modules are loaded before starting to
+       ;; compile files in parallel.
+       (compile #f)
        (par-for-each (lambda (file)
                        (compile-file* file mutex))
                      files)))))

guix/build/pull.scm

@@ -125,6 +125,9 @@ containing the source code.  Write any debugging output to DEBUG-PORT."
       (newline)
       (let ((mutex (make-mutex))
             (completed 0))
+        ;; Make sure compilation related modules are loaded before starting to
+        ;; compile files in parallel.
+        (compile #f)
         (par-for-each
          (lambda (file)
            (with-mutex mutex