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/compression.scm

@@ -920,10 +920,11 @@ tarballs.")
                  (base32
                   "1qxxsasvwbbbh6dl3138y9h3fg0q2v7xdk5jjc690bdg7g1wrj6n"))
                 (modules '((guix build utils)))
-                (snippet
-                 ;; This is a recursive submodule that is unnecessary for this
-                 ;; package, so delete it.
-                 '(delete-file-recursively "brotli/terryfy"))))
+                (snippet '(begin
+                            ;; This is a recursive submodule that is
+                            ;; unnecessary for this package, so delete it.
+                            (delete-file-recursively "brotli/terryfy")
+                            #t))))
       (build-system gnu-build-system)
       (native-inputs
        `(("autoconf" ,autoconf)
@@ -982,7 +983,9 @@ respectively, based on the reference implementation from Google.")
        (file-name (string-append name "-" version ".tar.gz"))
        (snippet
         ;; This file isn't freely distributable and has no effect on building.
-        '(delete-file "xdelta3/draft-korn-vcdiff.txt"))))
+        '(begin
+           (delete-file "xdelta3/draft-korn-vcdiff.txt")
+           #t))))
     (build-system gnu-build-system)
     (native-inputs
      `(("autoconf" ,autoconf)
@@ -1450,7 +1453,9 @@ handles the 7z format which features very high compression ratios.")
                 (modules '((guix build utils)))
                 (snippet
                  ;; Remove pre-compiled object.
-                 '(delete-file "gzstream.o"))))
+                 '(begin
+                    (delete-file "gzstream.o")
+                    #t))))
     (build-system gnu-build-system)
     (arguments
      `(#:test-target "test"
@@ -1487,7 +1492,9 @@ functionality in a C++ iostream.")
        (modules '((guix build utils)))
        (snippet
         ;; Delete irrelevant pre-compiled binaries.
-        '(for-each delete-file (find-files "." "\\.exe$")))))
+        '(begin
+           (for-each delete-file (find-files "." "\\.exe$"))
+           #t))))
     (build-system gnu-build-system)
     (arguments
      `(#:phases