gnu: Use invoke and return #t from all builders.

* gnu/packages/admin.scm, gnu/packages/android.scm, gnu/packages/audio.scm,
gnu/packages/avr.scm, gnu/packages/base.scm, gnu/packages/bioinformatics.scm,
gnu/packages/certs.scm, gnu/packages/check.scm, gnu/packages/code.scm,
gnu/packages/commencement.scm, gnu/packages/dictionaries.scm,
gnu/packages/docbook.scm, gnu/packages/emacs.scm, gnu/packages/embedded.scm,
gnu/packages/fonts.scm, gnu/packages/games.scm, gnu/packages/gnome.scm,
gnu/packages/gnu-doc.scm, gnu/packages/guile.scm, gnu/packages/hurd.scm,
gnu/packages/javascript.scm, gnu/packages/libreoffice.scm,
gnu/packages/linux.scm, gnu/packages/lisp.scm, gnu/packages/lxde.scm,
gnu/packages/mail.scm, gnu/packages/markup.scm, gnu/packages/mate.scm,
gnu/packages/pkg-config.scm, gnu/packages/qt.scm, gnu/packages/rust.scm,
gnu/packages/scheme.scm, gnu/packages/sdl.scm, gnu/packages/statistics.scm,
gnu/packages/syncthing.scm, gnu/packages/tex.scm, gnu/packages/web.scm,
gnu/packages/wine.scm, gnu/packages/xfce.scm: In the builders of packages
using 'trivial-build-system', use invoke where appropriate, raise exceptions
on errors, and otherwise return #t.

gnu/packages/lisp.scm

@@ -1231,7 +1231,8 @@ multiple inspectors with independent history.")
                          (assoc-ref %outputs "image")
                          "/bin/slynk")
                         %outputs
-                        #:dependencies ',slynk-systems)))))))
+                        #:dependencies ',slynk-systems))
+         #t)))))
 
 (define-public ecl-slynk
   (package
@@ -1253,7 +1254,8 @@ multiple inspectors with independent history.")
          (match %build-inputs
            (((names . paths) ...)
             (union-build (assoc-ref %outputs "out")
-                         paths))))))))
+                         paths)
+            #t)))))))
 
 (define-public sbcl-stumpwm+slynk
   (package