gnu: Use 'search-input-file' when looking for executables.

* gnu/packages/admin.scm (isc-dhcp): Use 'search-input-file' when
looking for executables.
* gnu/packages/audio.scm (ableton-link): Likewise.
* gnu/packages/benchmark.scm (fio): Likewise.
* gnu/packages/bioinformatics.scm (roary): Likewise.
(ngless): Likewise.
* gnu/packages/boost.scm (boost-for-irods): Likewise.
* gnu/packages/bootloaders.scm (grub): Likewise.
(grub-efi): Likewise.
* gnu/packages/chemistry.scm (inchi): Likewise.
* gnu/packages/dictionaries.scm (ding): Likewise.
* gnu/packages/dlang.scm (ldc): Likewise.
* gnu/packages/education.scm (childsplay): Likewise.
* gnu/packages/emacs-xyz.scm (emacs-hyperbole): Likewise.
(emacs-haskell-mode): Likewise.
(emacs-auctex): Likewise.
(emacs-ggtags): Likewise.
(emacs-graphviz-dot-mode): Likewise.
(emacs-flycheck-grammalecte): Likewise.
(emacs-counsel-notmuch): Likewise.
(emacspeak): Likewise.
(emacs-exwm): Likewise.
(emacs-exwm-x): Likewise.
(emacs-treemacs): Likewise.
(emacs-telega): Likewise.
(emacs-exiftool): Likewise.
* gnu/packages/emulators.scm (higan): Likewise.
* gnu/packages/engineering.scm (freehdl): Likewise.
(librepcb): Likewise.
* gnu/packages/entr.scm (entr): Likewise.
* gnu/packages/file-systems.scm (libeatmydata): Likewise.
(xfstests): Likewise.
(mergerfs): Likewise.
(mergerfs-tools): Likewise.
* gnu/packages/finance.scm (monero-gui): Likewise.
* gnu/packages/flashing-tools.scm (flashrom): Likewise.
* gnu/packages/fontutils.scm (fontforge): Likewise.
* gnu/packages/game-development.scm (python2-renpy): Likewise.
* gnu/packages/games.scm (opensurge): Likewise.
(xboard): Likewise.
(hyperrogue): Likewise.
(flare-game): Likewise.
(chessx): Likewise.
* gnu/packages/geo.scm (grass): Likewise.
* gnu/packages/glib.scm (glib): Likewise.
* gnu/packages/gnome.scm (mm-common): Likewise.
(network-manager-openvpn): Likewise.
(network-manager-vpnc): Likewise.
(network-manager-openconnect): Likewise.
(apostrophe): Likewise.
* gnu/packages/gnupg.scm (pius): Likewise.
(jetring): Likewise.
* gnu/packages/gnuzilla.scm (icedove): Likewise.
* gnu/packages/golang.scm (go-1.4): Likewise.
* gnu/packages/graphviz.scm (xdot): Likewise.
* gnu/packages/guile-xyz.scm (jupyter-guile-kernel): Likewise.
* gnu/packages/haskell-xyz.scm (ghc-hindent): Likewise.
* gnu/packages/ibus.scm (ibus): Likewise.
* gnu/packages/image.scm (phockup): Likewise.
* gnu/packages/irc.scm (quassel): Likewise.
* gnu/packages/java.scm (drip): Likewise.
(ant-bootstrap): Likewise.
(tla2tools): Likewise.
* gnu/packages/julia.scm (julia): Likewise.
* gnu/packages/less.scm (lesspipe): Likewise.
* gnu/packages/libreoffice.scm (libreoffice): Likewise.
* gnu/packages/linux.scm (fuse): Likewise.
(lm-sensors): Likewise.
(bluez): Likewise.
(fakeroot): Likewise.
(inputattach): Likewise.
* gnu/packages/lisp-xyz.scm (sbcl-cl-diskspace): Likewise.
* gnu/packages/lisp.scm (lisp-repl-core-dumper): Likewise.
* gnu/packages/lua.scm (fennel): Likewise.
* gnu/packages/lxde.scm (spacefm): Likewise.
* gnu/packages/mail.scm (public-inbox): Likewise.
* gnu/packages/maths.scm (hdf-java): Likewise.
(maxima): Likewise.
(frama-c): Likewise.
* gnu/packages/messaging.scm (libgadu): Likewise.
* gnu/packages/music.scm (denemo): Likewise.
(curseradio): Likewise.
* gnu/packages/netpbm.scm (netpbm): Likewise.
* gnu/packages/networking.scm (blueman): Likewise.
(squid): Likewise.
(aircrack-ng): Likewise.
* gnu/packages/node.scm (node): Likewise.
(node-llparse-frontend-bootstrap): Likewise.
(node-llparse-bootstrap): Likewise.
(llhttp-bootstrap): Likewise.
(node-lts): Likewise.
* gnu/packages/ocaml.scm (ocaml-4.11): Likewise.
(opam): Likewise.
(ocaml-graph): Likewise.
* gnu/packages/orpheus.scm (orpheus): Likewise.
* gnu/packages/password-utils.scm (password-store): Likewise.
* gnu/packages/python.scm (pypy3): Likewise.
* gnu/packages/qt.scm (qt5ct): Likewise.
* gnu/packages/radio.scm (libosmo-dsp): Likewise.
* gnu/packages/ruby.scm (ruby-pandoc-ruby): Likewise.
* gnu/packages/rust.scm (rust-1.30): Likewise.
* gnu/packages/screen.scm (byobu): Likewise.
* gnu/packages/statistics.scm (r-with-tests): Likewise.
* gnu/packages/suckless.scm (surf): Likewise.
* gnu/packages/syndication.scm (gfeeds): Likewise.
* gnu/packages/telephony.scm (mumble): Likewise.
* gnu/packages/terminals.scm (alacritty): Likewise.
* gnu/packages/tex.scm (texlive-bin): Likewise.
* gnu/packages/uml.scm (plantuml): Likewise.
* gnu/packages/version-control.scm (python-git-multimail): Likewise.
(gitolite): Likewise.
(hg-commitsigs): Likewise.
(git-when-merged): Likewise.
(git-imerge): Likewise.
(gita): Likewise.
* gnu/packages/video.scm (you-get): Likewise.
* gnu/packages/vim.scm (eovim): Likewise.
* gnu/packages/virtualization.scm (qemu): Likewise.
(virt-manager): Likewise.
(criu): Likewise.
* gnu/packages/vpn.scm (strongswan): Likewise.
(xl2tpd): Likewise.
* gnu/packages/wm.scm (i3lock-fancy): Likewise.
* gnu/packages/wxwidgets.scm (python-wxpython): Likewise.
(python2-wxpython): Likewise.
* gnu/packages/xdisorg.scm (autorandr): Likewise.
* gnu/packages/xorg.scm (hackneyed-x11-cursors): Likewise.
(v86d): Likewise.
(mkfontdir): Likewise.
(xpra): Likewise.

gnu/packages/version-control.scm

@@ -1,7 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
 ;;; Copyright © 2013 Cyril Roelandt <tipecaml@gmail.com>
-;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2013, 2014 Andreas Enge <andreas@enge.fr>
 ;;; Copyright © 2015, 2016 Mathieu Lirzin <mthl@gnu.org>
 ;;; Copyright © 2014, 2015, 2016 Mark H Weaver <mhw@netris.org>
@@ -1035,9 +1035,8 @@ a built-in cache to decrease server I/O pressure.")
                                (assoc-ref inputs "git") "/bin/git"
                                "'"))
                (("/usr/sbin/sendmail")
-                (string-append (assoc-ref inputs "sendmail")
-                               "/usr/sbin/sendmail")))
-             #t)))))
+                (search-input-file inputs
+                                   "/usr/sbin/sendmail"))))))))
     (inputs
      `(("git" ,git)
        ("sendmail" ,sendmail)))
@@ -1424,8 +1423,7 @@ also walk each side of a merge and test those changes individually.")
                   (delete 'build)
                   (add-before 'install 'patch-scripts
                     (lambda* (#:key inputs #:allow-other-keys)
-                      (let ((perl (string-append (assoc-ref inputs "perl")
-                                                 "/bin/perl")))
+                      (let ((perl (search-input-file inputs "/bin/perl")))
                         ;; This seems to take care of every shell script that
                         ;; invokes Perl.
                         (substitute* (find-files "." ".*")
@@ -1462,8 +1460,7 @@ also walk each side of a merge and test those changes individually.")
                       (substitute* '("src/lib/Gitolite/Hooks/PostUpdate.pm"
                                      "src/lib/Gitolite/Hooks/Update.pm")
                         (("/usr/bin/perl")
-                         (string-append (assoc-ref inputs "perl")
-                                        "/bin/perl")))
+                         (search-input-file inputs "/bin/perl")))
 
                       (substitute* "src/lib/Gitolite/Common.pm"
                         (("\"ssh-keygen")
@@ -1759,10 +1756,8 @@ history.  It implements the changeset evolution concept for Mercurial.")
          (modify-phases %standard-phases
            (add-after 'unpack 'patch-paths
            (lambda* (#:key inputs #:allow-other-keys)
-             (let ((gpg (string-append (assoc-ref inputs "gnupg")
-                                       "/bin/gpg"))
-                   (openssl (string-append (assoc-ref inputs "openssl")
-                                           "/bin/openssl")))
+             (let ((gpg (search-input-file inputs "/bin/gpg"))
+                   (openssl (search-input-file inputs "/bin/openssl")))
                (substitute* "commitsigs.py"
                  (("b'gpg',") (string-append "b'" gpg "',"))
                  (("b'openssl',") (string-append "b'" openssl "',")))))))
@@ -2707,8 +2702,7 @@ directory full of HOWTOs.")
                #t))
            (add-before 'install 'patch-git
              (lambda* (#:key inputs #:allow-other-keys)
-               (let ((git (string-append (assoc-ref inputs "git")
-                                         "/bin/git")))
+               (let ((git (search-input-file inputs "/bin/git")))
                  (substitute* "bin/git-when-merged"
                    (("'git'") (string-append "'" git "'")))
                  #t)))
@@ -2752,8 +2746,7 @@ how information about the merge is displayed.")
          (delete 'configure)
          (add-before 'install 'patch-git
            (lambda* (#:key inputs #:allow-other-keys)
-             (let ((git (string-append (assoc-ref inputs "git")
-                                       "/bin/git")))
+             (let ((git (search-input-file inputs "/bin/git")))
                (substitute* "git-imerge"
                  (("'git'") (string-append "'" git "'")))
                #t)))
@@ -3045,11 +3038,10 @@ defects faster.")
                (substitute* "tests/test_main.py"
                  (("'gita\\\\n'") "'source\\n'")
                  (("'gita'") "'source'"))
-               (invoke (string-append (assoc-ref inputs "git") "/bin/git")
+               (invoke (search-input-file inputs "/bin/git")
                        "init")
                (add-installed-pythonpath inputs outputs)
-               (invoke (string-append (assoc-ref inputs "python-pytest")
-                                      "/bin/pytest")
+               (invoke (search-input-file inputs "/bin/pytest")
                        "-vv" "tests")))
            (add-after 'install 'install-shell-completions
              (lambda* (#:key outputs #:allow-other-keys)