ui: ‘show-what-to-build’ displays builds in topological order.

That gives something like:

  $ ./pre-inst-env guix build vim --no-grafts --no-substitutes -n
  The following derivations would be built:
    /gnu/store/…-tcsh-6.24.01.tar.gz.drv
    /gnu/store/…-tcsh-6.24.01.tar.zst.drv
    /gnu/store/…-tcsh-6.24.01.drv
    /gnu/store/…-vim-9.1.0744-checkout.drv
    /gnu/store/…-vim-9.1.0744.drv

… with the derivation(s) being asked for coming last.

* guix/ui.scm (show-what-to-build): Reverse ‘build/full’ before folding it.

Change-Id: Ic0da9f4f8a58c7ed5e2d10f6ec2226f0865aed75

guix/ui.scm

@@ -1077,7 +1077,7 @@ summary, and level 0 shows nothing."
                                          #:hook ,hook
                                          #:build ,(cons file build))))))))
                               '(#:graft () #:hook () #:build ())
-                              build/full)
+                              (reverse! build/full)) ;preserve ordering
                    ((#:graft graft #:hook hook #:build build)
                     (values graft hook build)))))
     (define installed-size