gnu: emacs: Add coreutils and gzip to PATH.

Some parts of Emacs (dired, compression handling, Tramp) shell out to commands
and patching them all is a daunting task.  Also, w.r.t. Tramp, we need those
commands to be portable across multiple machines, which need not only be Guix
machines (and even if they are, store items can be different).  This patch
ensures a ‘sane’ setup FSVO ‘sane’.

* gnu/packages/emacs.scm (emacs)[wrap-load-path]: Rename to...
[wrap-emacs-paths] ... this.  Also patch PATH.

gnu/packages/emacs.scm

@@ -201,8 +201,8 @@
                 (car (find-files "bin" "^emacs-([0-9]+\\.)+[0-9]+$"))
                 "bin/emacs")
                #t)))
-         (add-after 'strip-double-wrap 'wrap-load-path
-           (lambda* (#:key outputs #:allow-other-keys)
+         (add-after 'strip-double-wrap 'wrap-emacs-paths
+           (lambda* (#:key inputs outputs #:allow-other-keys)
              (let* ((out (assoc-ref outputs "out"))
                     (lisp-dirs (find-files (string-append out "/share/emacs")
                                            "^lisp$"
@@ -210,6 +210,13 @@
                (for-each
                 (lambda (prog)
                   (wrap-program prog
+                    ;; emacs-next and variants rely on uname being in PATH for
+                    ;; Tramp.  Tramp paths can't be hardcoded, because they
+                    ;; need to be portable.
+                    `("PATH" suffix
+                      ,(map (lambda (in) (string-append in "/bin"))
+                            (list (assoc-ref inputs "gzip")
+                                  (assoc-ref inputs "coreutils"))))
                     `("EMACSLOADPATH" suffix ,lisp-dirs)))
                 (find-files (string-append out "/bin")
                             ;; Matches versioned and unversioned emacs binaries.
@@ -231,6 +238,10 @@
      `(("gnutls" ,gnutls)
        ("ncurses" ,ncurses)
 
+       ;; Required for "core" functionality, such as dired and compression.
+       ("coreutils" ,coreutils)
+       ("gzip" ,gzip)
+
        ;; Avoid Emacs's limited movemail substitute that retrieves POP3 email
        ;; only via insecure channels.  This is not needed for (modern) IMAP.
        ("mailutils" ,mailutils)
@@ -361,7 +372,9 @@ also enabled and works without glitches even on X server."))))
            (delete 'strip-double-wrap)))))
     (inputs
      `(("guix-emacs.el" ,(search-auxiliary-file "emacs/guix-emacs.el"))
-       ("ncurses" ,ncurses)))
+       ("ncurses" ,ncurses)
+       ("coreutils" ,coreutils)
+       ("gzip" ,gzip)))
     (native-inputs
      `(("pkg-config" ,pkg-config)))))