gnu: Remove '%final-inputs' references at the top level.

Due to circular dependencies, referring to bindings exported by other
modules from the top level is frowned upon.  This patch addresses one of
the remaining cases.

* gnu/packages/base.scm (%final-inputs): New procedure.
* gnu/packages/cross-base.scm: Remove (gnu packages commencement) import.
(cross-gcc): Use the new '%final-inputs'.
* gnu/packages/make-bootstrap.scm: Remove (gnu packages commencement) import.
(package-with-relocatable-glibc): Use the new '%final-inputs'.

gnu/packages/base.scm

@@ -1003,4 +1003,10 @@ program.  It supports a wide variety of different encodings.")
          (proc  (module-ref iface 'canonical-package)))
     (proc package)))
 
+(define-public (%final-inputs)
+  "Return the list of \"final inputs\"."
+  ;; Avoid circular dependency by lazily resolving 'commencement'.
+  (let ((iface (resolve-interface '(gnu packages commencement))))
+    (module-ref iface '%final-inputs)))
+
 ;;; base.scm ends here

gnu/packages/cross-base.scm

@@ -23,7 +23,6 @@
   #:use-module (gnu packages)
   #:use-module (gnu packages gcc)
   #:use-module (gnu packages base)
-  #:use-module (gnu packages commencement)
   #:use-module (gnu packages linux)
   #:use-module (guix packages)
   #:use-module (guix download)
@@ -257,11 +256,11 @@ GCC that does not target a libc; otherwise, target that libc."
 
        ;; Call it differently so that the builder can check whether the "libc"
        ;; input is #f.
-       ("libc-native" ,@(assoc-ref %final-inputs "libc"))
+       ("libc-native" ,@(assoc-ref (%final-inputs) "libc"))
 
        ;; Remaining inputs.
        ,@(let ((inputs (append (package-inputs %xgcc)
-                               (alist-delete "libc" %final-inputs))))
+                               (alist-delete "libc" (%final-inputs)))))
            (if libc
                `(("libc" ,libc)
                  ("xkernel-headers"                ;the target headers

gnu/packages/make-bootstrap.scm

@@ -23,7 +23,6 @@
   #:use-module (guix build-system trivial)
   #:use-module (guix build-system gnu)
   #:use-module ((gnu packages) #:select (search-patch))
-  #:use-module ((gnu packages commencement) #:select (%final-inputs))
   #:use-module (gnu packages base)
   #:use-module (gnu packages cross-base)
   #:use-module (gnu packages bash)
@@ -101,14 +100,14 @@ for `sh' in $PATH, and without nscd, and with static NSS modules."
                                           (cross-binutils target)
                                           (cross-bootstrap-libc)))
             ("cross-binutils" ,(cross-binutils target))
-            ,@%final-inputs))
+            ,@(%final-inputs)))
         `(("libc" ,(glibc-for-bootstrap))
           ("gcc" ,(package (inherit gcc)
                     (outputs '("out")) ; all in one so libgcc_s is easily found
                     (inputs
                      `(("libc",(glibc-for-bootstrap))
                        ,@(package-inputs gcc)))))
-          ,@(fold alist-delete %final-inputs '("libc" "gcc")))))
+          ,@(fold alist-delete (%final-inputs) '("libc" "gcc")))))
 
   (package-with-explicit-inputs p inputs
                                 (current-source-location)