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/crypto.scm

@@ -181,7 +181,8 @@ OpenBSD tool of the same name.")
            (substitute* "src/crypto.cpp"
              (("argon2/argon2.h") "argon2.h"))
            (substitute* "configure.ac"
-             (("src/argon2/Makefile") ""))))
+             (("src/argon2/Makefile") ""))
+           #t))
        (sha256
         (base32
          "09yvkmbqbym3b5md4n96qc1s9sf2n8ji404hagih45rmsj49599x"))))
@@ -226,9 +227,11 @@ communication.")
          "1906254dg5hwljh0h4gyrw09ms3b57dlhjfzhfzffv50yzpkl837"))
        (modules '((guix build utils)))
        ;; Remove bundled dependencies in favour of proper inputs.
-       (snippet '(for-each delete-file-recursively
-                           (find-files "internal" "^tinyxml2-[0-9]"
-                                       #:directories? #t)))))
+       (snippet '(begin
+                   (for-each delete-file-recursively
+                             (find-files "internal" "^tinyxml2-[0-9]"
+                                         #:directories? #t))
+                   #t))))
     (build-system cmake-build-system)
     (native-inputs
      `(("gettext" ,gettext-minimal)
@@ -270,8 +273,10 @@ the wrong hands.")
          "1dmgjcf7mnwc6h72xkvpaqpzxw8vmlnsmzz0s27pg0giwzm3sp0i"))
        (modules '((guix build utils)))
        ;; Create relative symbolic links instead of absolute ones to /lib/*
-       (snippet '(substitute* "Makefile" (("\\$\\(LNS\\) \\$\\(LIBDIR\\)/")
-                                          "$(LNS) ")))))
+       (snippet '(begin
+                   (substitute* "Makefile" (("\\$\\(LNS\\) \\$\\(LIBDIR\\)/")
+                                            "$(LNS) "))
+                   #t))))
     (build-system gnu-build-system)
     (arguments
      `(#:phases (modify-phases %standard-phases