gnu: All snippets report errors using exceptions, else return #t.

* gnu/packages/admin.scm, gnu/packages/algebra.scm, gnu/packages/audio.scm,
gnu/packages/backup.scm, gnu/packages/base.scm,
gnu/packages/bioinformatics.scm, gnu/packages/cdrom.scm,
gnu/packages/chez.scm, gnu/packages/code.scm, gnu/packages/compression.scm,
gnu/packages/cross-base.scm, gnu/packages/crypto.scm, gnu/packages/cups.scm,
gnu/packages/databases.scm, gnu/packages/dns.scm, gnu/packages/emacs.scm,
gnu/packages/emulators.scm, gnu/packages/engineering.scm,
gnu/packages/enlightenment.scm, gnu/packages/fpga.scm,
gnu/packages/freedesktop.scm, gnu/packages/ftp.scm, gnu/packages/games.scm,
gnu/packages/gcc.scm, gnu/packages/geo.scm, gnu/packages/ghostscript.scm,
gnu/packages/gl.scm, gnu/packages/glib.scm, gnu/packages/gnome.scm,
gnu/packages/gnuzilla.scm, gnu/packages/graphics.scm, gnu/packages/gtk.scm,
gnu/packages/guile.scm, gnu/packages/irc.scm, gnu/packages/java.scm,
gnu/packages/kerberos.scm, gnu/packages/linux.scm, gnu/packages/lisp.scm,
gnu/packages/lxde.scm, gnu/packages/machine-learning.scm,
gnu/packages/mail.scm, gnu/packages/maths.scm, gnu/packages/messaging.scm,
gnu/packages/monitoring.scm, gnu/packages/mp3.scm, gnu/packages/music.scm,
gnu/packages/netpbm.scm, gnu/packages/networking.scm, gnu/packages/node.scm,
gnu/packages/nvi.scm, gnu/packages/ocaml.scm, gnu/packages/pdf.scm,
gnu/packages/perl.scm, gnu/packages/php.scm, gnu/packages/plotutils.scm,
gnu/packages/pretty-print.scm, gnu/packages/profiling.scm,
gnu/packages/pulseaudio.scm, gnu/packages/python-crypto.scm,
gnu/packages/python.scm, gnu/packages/qt.scm, gnu/packages/robotics.scm,
gnu/packages/sawfish.scm, gnu/packages/scanner.scm, gnu/packages/scheme.scm,
gnu/packages/scribus.scm, gnu/packages/sdl.scm,
gnu/packages/serialization.scm, gnu/packages/shells.scm,
gnu/packages/slang.scm, gnu/packages/smalltalk.scm, gnu/packages/ssh.scm,
gnu/packages/sync.scm, gnu/packages/syncthing.scm, gnu/packages/tbb.scm,
gnu/packages/terminals.scm, gnu/packages/texinfo.scm,
gnu/packages/text-editors.scm, gnu/packages/textutils.scm,
gnu/packages/tls.scm, gnu/packages/unrtf.scm,
gnu/packages/version-control.scm, gnu/packages/video.scm,
gnu/packages/vpn.scm, gnu/packages/web.scm, gnu/packages/wm.scm,
gnu/packages/wxwidgets.scm, gnu/packages/xdisorg.scm, gnu/packages/xorg.scm:
In all snippets, report errors using exceptions, or else return #t.

gnu/packages/plotutils.scm

@@ -60,9 +60,11 @@
               ;; that, libplot.la ends up containing just "-lXaw" (without
               ;; "-L/path/to/Xaw"), due to the fact that there is no
               ;; libXaw.la, which forces us to propagate libXaw.
-              '(substitute* "configure"
-                 (("-lXaw")
-                  "-lXaw7")))))
+              '(begin
+                 (substitute* "configure"
+                   (("-lXaw")
+                    "-lXaw7"))
+                 #t))))
     (build-system gnu-build-system)
     (inputs `(("libpng" ,libpng)
               ("libx11" ,libx11)
@@ -97,7 +99,8 @@ scientific data.")
                   ;; Use the standard location for modules.
                   (substitute* "Makefile.in"
                     (("godir = .*$")
-                     "godir = $(moddir)\n"))))))
+                     "godir = $(moddir)\n"))
+                  #t))))
     (build-system gnu-build-system)
     (native-inputs `(("pkg-config" ,pkg-config)))
     (inputs `(("guile" ,guile-2.2)))
@@ -123,9 +126,11 @@ using the Cairo drawing library.")
               (modules '((guix build utils)))
               (snippet
                ;; Install binaries in the right place.
-               '(substitute* "src/Makefile"
-                  (("INSTALLBIN =.*$")
-                   (string-append "INSTALLBIN = $(out)/bin"))))))
+               '(begin
+                  (substitute* "src/Makefile"
+                    (("INSTALLBIN =.*$")
+                     (string-append "INSTALLBIN = $(out)/bin")))
+                  #t))))
     (build-system gnu-build-system)
     (arguments
      '(#:tests? #f