gnu: commencement: Further optimize the package object graph.

For a package like:

  (define-public xxx
    (package
      (inherit (@ (gnu packages base) coreutils))
      (name "xxx")
      (inputs (@ (gnu packages commencement) %final-inputs))
      (native-inputs '())
      (propagated-inputs '())
      (arguments '(#:implicit-inputs? #f))))

this reduces the package object graph from 176 nodes (1852 edges) to 113
nodes (1114 edges).

The number of 'add-data-to-store' calls in "guix build coreutils -nd"
drops from 2045 to 1301, and the number of memoization tables drops from
102 to 40.

"guix build libreoffice -nd" goes from 2.40s to 2.27s.

* gnu/packages/commencement.scm (with-boot4): New variable.
(guile-final, glibc-utf8-locales-final): Use it.
(with-boot4, with-boot5): New variable.
(gnu-make-final): Rewrite to avoid 'package-with-explicit-inputs'.
(coreutils-final): Use 'with-boot5' instead of
'package-with-explicit-inputs'.
(grep-final): Likewise.
(with-boot6): New variable.
(sed-final, %final-inputs): Use it.

gnu/packages/commencement.scm

@@ -2365,14 +2365,14 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
   `(("bash" ,bash-final)
     ,@(alist-delete "bash" (%boot3-inputs))))
 
+(define with-boot4
+  (package-with-explicit-inputs %boot4-inputs %bootstrap-guile))
+
 (define-public guile-final
   ;; This package must be public because other modules refer to it.  However,
   ;; mark it as hidden so that 'fold-packages' ignores it.
-  (package-with-bootstrap-guile
+  (with-boot4 (hidden-package
-   (package-with-explicit-inputs (hidden-package guile-2.2/fixed)
+               (package-with-bootstrap-guile guile-2.2/fixed))))
-                                 %boot4-inputs
-                                 (current-source-location)
-                                 #:guile %bootstrap-guile)))
 
 (define glibc-utf8-locales-final
   ;; Now that we have GUILE-FINAL, build the UTF-8 locales.  They are needed
@@ -2384,10 +2384,7 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
     (inherit glibc-utf8-locales)
     (native-inputs
      `(("glibc" ,glibc-final)
-       ("gzip"
+       ("gzip" ,(with-boot4 gzip))))))
-        ,(package-with-explicit-inputs gzip %boot4-inputs
-                                       (current-source-location)
-                                       #:guile %bootstrap-guile))))))
 
 (define-public ld-wrapper
   ;; The final 'ld' wrapper, which uses the final Guile and Binutils.
@@ -2403,35 +2400,45 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
   `(("locales" ,glibc-utf8-locales-final)
     ,@(%boot4-inputs)))
 
+(define with-boot5
+  (package-with-explicit-inputs %boot5-inputs))
+
 (define gnu-make-final
   ;; The final GNU Make, which uses the final Guile.
-  (package-with-explicit-inputs (package-with-bootstrap-guile gnu-make)
+  ;; FIXME: This is a mistake: we shouldn't be propagating GUILE-FINAL to
-                                (lambda _
+  ;; PKG-CONFIG.
-                                  `(("guile" ,guile-final)
+  ;; TODO: Fix that on the next rebuild cycle.
-                                    ,@(%boot5-inputs)))
+  (let ((pkg-config (package
-                                (current-source-location)))
+                      (inherit pkg-config)
+                      (inputs `(("guile" ,guile-final)
+                                ,@(%boot5-inputs)))
+                      (arguments
+                       `(#:implicit-inputs? #f
+                         ,@(package-arguments pkg-config))))))
+    (package
+      (inherit (package-with-bootstrap-guile gnu-make))
+      (inputs `(("guile" ,guile-final)
+                ,@(%boot5-inputs)))
+      (native-inputs `(("pkg-config" ,pkg-config)))
+      (arguments
+       `(#:implicit-inputs? #f
+         ,@(package-arguments gnu-make))))))
+
 
 (define coreutils-final
   ;; The final Coreutils.  Treat them specially because some packages, such as
   ;; Findutils, keep a reference to the Coreutils they were built with.
-  (package-with-explicit-inputs (package-with-bootstrap-guile coreutils)
+  (with-boot5 (package-with-bootstrap-guile coreutils)
-                                %boot5-inputs
+              ;; Use the final Guile, linked against the
-                                (current-source-location)
+              ;; final libc with working iconv, so that
-
+              ;; 'substitute*' works well when touching
-                                ;; Use the final Guile, linked against the
+              ;; test files in Gettext.
-                                ;; final libc with working iconv, so that
+              ))
-                                ;; 'substitute*' works well when touching
-                                ;; test files in Gettext.
-                                #:guile guile-final))
 
 (define grep-final
   ;; The final grep.  Gzip holds a reference to it (via zgrep), so it must be
   ;; built before gzip.
-  (let ((grep (package-with-explicit-inputs
+  (let ((grep (with-boot5 (package-with-bootstrap-guile grep))))
-               (package-with-bootstrap-guile grep)
-               %boot5-inputs
-               (current-source-location)
-               #:guile guile-final)))
     (package/inherit grep
                      (inputs (alist-delete "pcre" (package-inputs grep)))
                      (native-inputs `(("perl" ,perl-boot0))))))
@@ -2442,12 +2449,12 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
     ("grep" ,grep-final)
     ,@(%boot5-inputs)))
 
+(define with-boot6
+  (package-with-explicit-inputs %boot6-inputs))
+
 (define sed-final
   ;; The final sed.
-  (let ((sed (package-with-explicit-inputs (package-with-bootstrap-guile sed)
+  (let ((sed (with-boot6 (package-with-bootstrap-guile sed))))
-                                           %boot6-inputs
-                                           (current-source-location)
-                                           #:guile guile-final)))
     (package/inherit sed (native-inputs `(("perl" ,perl-boot0))))))
 
 (define-public %final-inputs
@@ -2455,8 +2462,7 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
   ;; still use 'package-with-bootstrap-guile' so that the bootstrap tools are
   ;; used for origins that have patches, thereby avoiding circular
   ;; dependencies.
-  (let ((finalize (compose (cut package-with-explicit-inputs <> %boot6-inputs
+  (let ((finalize (compose with-boot6
-                                (current-source-location))
                            package-with-bootstrap-guile)))
     `(,@(map (match-lambda
                ((name package)