gnu: linux-libre: Update to 4.1.6.

* gnu/packages/linux.scm (linux-libre): Update to 4.1.6.

gnu: tk: Build with Xft support.

* gnu/packages/tcl.scm (tk)[inputs]: Add LIBXFT.
  [native-inputs]: New field.

gnu: Add Rage player.

* gnu/packages/enlightenment.scm: Add Rage.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

build: ruby: Rewrite build system to use gem archives.

Co-Authored-By: Pjotr Prins <pjotr.public01@thebird.nl>

* guix/build-system/ruby.scm (lower): Remove git dependency.
  (rubygems-uri): New procedure.
* guix/build/ruby-build-system (gitify): Delete.
  (unpack): Use 'gem unpack' utility.
  (check): Add docstring.
  (build): Repack modified gem.
  (install): Rebuild unpacked gem and install it.
  (%standard-phases): Remove gitify and build phases.
* gnu/packages/ruby.scm (ruby-hoe, ruby-rake-compiler, ruby-i18n,
  ruby-rspec-support, ruby-rspec-core, ruby-diff-lcs-for-rspec,
  ruby-rspec-expectations, ruby-rspec-mocks, ruby-rspec, bundler,
  ruby-useragent, ruby-bacon, ruby-arel, ruby-connection-pool,
  ruby-net-http-persistent, ruby-minitest, ruby-minitest-sprint,
  ruby-minitest-bacon, ruby-daemons, ruby-git, ruby-slop,
  ruby-multipart-post): Convert to new build system.
* doc/guix.texi (ruby-build-system): Document the gem archive requirement.

gnu: calibre: Update to 2.35.0.

* gnu/packages/ebook.scm (calibre): Update to 2.35.0.

syscalls: setns: Skip binding if there is no such C function.

On systems with a glibc prior to 2.14, the 'setns' function is not available.

Thanks to Eric Bavier for reporting the issue.

* guix/build/syscalls.scm (setns): Wrap with 'false-if-exception'.

gnu: r: Add R_LIBS_SITE to native-search-paths.

* gnu/packages/statistics.scm (r)[native-search-paths]: Add
  specification for "R_LIBS_SITE" variable.

gnu: r: Update to 3.2.2.

* gnu/packages/statistics.scm (r): Update to 3.2.2.

gnu: Add American fuzzy lop.

* gnu/packages/debug.scm (american-fuzzy-lop): New variable.

gnu: qemu: Honor #:configure-flags argument.

* gnu/packages/qemu.scm (qemu-headless)[arguments]: Honor #:configure-flags
  arguments for configure phase.

gnu: ardour: Update to 4.2.

* gnu/packages/audio.scm (ardour): Update to 4.2.

gnu: notmuch: Update to 0.20.2.

* gnu/packages/mail.scm (notmuch): Update to 0.20.2.  Add python-sphinx native
  input.  Rewrite phases using 'modify-phases' syntax.

gnu: offlineimap: Update to 6.5.7.

* gnu/packages/mail.scm (offlineimap): Update to 6.5.7.

gnu: guitarix: Update to 0.33.0.

* gnu/packages/audio.scm (guitarix): Update to 0.33.0.
  [native-inputs]: Add faust.

gnu: Add znc.

* gnu/packages/messaging.scm (znc): New variable.

gnu: Remove mplayer2.

* gnu/packages/video.scm (mplayer2): Removed variable.

gnu: epiphany: Add dconf to propagated-inputs.

* gnu/packages/gnome.scm (epiphany)[propagated-inputs]: New field.

gnu: flint: Disable parallel tests.

* gnu/packages/algebra.scm (flint)[arguments]: Disable parallel tests,
  which makes the build pass on arm.

gnu: Add Gamine.

* gnu/packages/games.scm (gamine): New variable.

gnu: glib-networking: Prefer 'SSL_CERT_FILE' as TLS CA file.

This is an improvement over commit af6100f.

* gnu/packages/gnome.scm (glib-networking)[source](patches): New field.
  [arguments]: Pass '/etc/ssl/certs/ca-certificates.crt' to configure.
  Set 'SSL_CERT_FILE' to '/dev/null' in 'use-empty-ssl-cert-file' phase.
  (libsoup)[arguments]: Set 'SSL_CERT_FILE' to '/dev/null' in
  'pre-check' phase.
* gnu/packages/patches/glib-networking-ssl-cert-file.patch: New patch.
* gnu-system.am (dist_patch_DATA): Add it.