doc: Reword "The GCC toolchain".

Fix commit 1f14e25c1969a93908288cb302a572f3cbbaa478
as discussed in <https://bugs.gnu.org/41038>.

* doc/guix.texi (Packages for C Development): Rename to...
(The GCC toolchain): ...this. Add gfortran-toolchain.
(Invoking guix package): Add guix-search anchor.
(Application Setup)[The GCC toolchain]: Remove.

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

etc: Add a systemd unit to bind-mount @storedir@ read-only.

* etc/gnu-store.mount.in: New file.
* nix/local.mk (nodist_systemdservice_DATA): Add it.
(etc/%.mount): New rule for it.
* etc/guix-install.sh (sys_enable_guix_daemon): Install it.
* doc/guix.texi (Binary Installation): Document it.
* .gitignore: Ignore changes to it.

gexp: Add 'let-system'.

* guix/gexp.scm (<system-binding>): New record type.
(let-system): New macro.
(system-binding-compiler): New procedure.
(default-expander): Add 'self-quoting?' case.
(self-quoting?): New procedure.
(lower-inputs): Add 'filterm'.  Pass the result of
'mapm/accumulate-builds' through FILTERM.
(gexp->sexp)[self-quoting?]: Remove.
* tests/gexp.scm ("let-system", "let-system, target")
("let-system, ungexp-native, target")
("let-system, nested"): New tests.
* doc/guix.texi (G-Expressions): Document it.

pack: Add relocation via ld.so and fakechroot.

* gnu/packages/aux-files/run-in-namespace.c (HAVE_EXEC_WITH_LOADER): New
macro.
(bind_mount): Rename to...
(mirror_directory): ... this.  Add 'firmlink' argument and use it
instead of calling mkdir/open/close/mount directly.
(bind_mount, make_symlink): New functions.
(exec_in_user_namespace): Adjust accordingly.
(exec_with_loader) [HAVE_EXEC_WITH_LOADER]: New function.
(exec_performance): New function.
(engines): Add them.
* guix/scripts/pack.scm (wrapped-package)[fakechroot-library]
[audit-module]: New procedures.
[audit-source]: New variable.
[build](elf-interpreter, elf-loader-compile-flags): New procedures.
(build-wrapper): Use them.
* tests/guix-pack-relocatable.sh: Test with
'GUIX_EXECUTION_ENGINE=fakechroot'.
* doc/guix.texi (Invoking guix pack): Document the 'performance' and
'fakechroot' engines.
* gnu/packages/aux-files/pack-audit.c: New file.
* Makefile.am (AUX_FILES): Add it.

pack: Wrapper honors 'GUIX_EXECUTION_ENGINE' environment variable.

* gnu/packages/aux-files/run-in-namespace.c (struct engine): New type.
(exec_default): New function.
(engines): New variable.
(execution_engine): New function.
(main): Use it instead of calling 'exec_in_user_namespace' and
'exec_with_proot' directly.
* tests/guix-pack-relocatable.sh: Add test with 'GUIX_EXECUTION_ENGINE'.
* doc/guix.texi (Invoking guix pack): Document 'GUIX_EXECUTION_ENGINE'.

doc: Mention guix-daemon's 'https_proxy' environment variable.

* doc/guix.texi (Proxy Settings, Derivations): Mention 'https_proxy'.

mailmap: Update entries for Nikita.

* .mailmap: change email and name for Nikita.
* Makefile.am, doc/guix.texi, etc/completion/fish/guix.fish,
gnu/packages/accessibility.scm, gnu/packages/admin.scm,
gnu/packages/audio.scm, gnu/packages/autotools.scm, gnu/packages/cdrom.scm,
gnu/packages/check.scm, gnu/packages/cinnamon.scm,
gnu/packages/compression.scm, gnu/packages/crypto.scm,
gnu/packages/databases.scm, gnu/packages/django.scm, gnu/packages/dns.scm,
gnu/packages/elixir.scm, gnu/packages/emacs-xyz.scm, gnu/packages/emacs.scm,
gnu/packages/enlightenment.scm, gnu/packages/erlang.scm,
gnu/packages/fonts.scm, gnu/packages/fontutils.scm, gnu/packages/forth.scm,
gnu/packages/fvwm.scm, gnu/packages/games.scm, gnu/packages/gl.scm,
gnu/packages/gnome.scm, gnu/packages/gnunet.scm, gnu/packages/gnupg.scm,
gnu/packages/gtk.scm, gnu/packages/guile-wm.scm, gnu/packages/guile-xyz.scm,
gnu/packages/haskell-apps.scm, gnu/packages/haskell-check.scm,
gnu/packages/haskell-crypto.scm, gnu/packages/haskell-xyz.scm,
gnu/packages/haskell.scm, gnu/packages/image-viewers.scm,
gnu/packages/image.scm, gnu/packages/irc.scm, gnu/packages/language.scm,
gnu/packages/libcanberra.scm, gnu/packages/linux.scm,
gnu/packages/lisp-xyz.scm, gnu/packages/lisp.scm, gnu/packages/lolcode.scm,
gnu/packages/lxde.scm, gnu/packages/lxqt.scm, gnu/packages/mail.scm,
gnu/packages/markup.scm, gnu/packages/mate.scm, gnu/packages/maths.scm,
gnu/packages/mc.scm, gnu/packages/messaging.scm, gnu/packages/music.scm,
gnu/packages/ncurses.scm, gnu/packages/networking.scm,
gnu/packages/nickle.scm, gnu/packages/openbox.scm, gnu/packages/pdf.scm,
gnu/packages/perl-check.scm, gnu/packages/perl.scm,
gnu/packages/python-compression.scm, gnu/packages/python-crypto.scm,
gnu/packages/python-web.scm, gnu/packages/python-xyz.scm,
gnu/packages/python.scm, gnu/packages/qt.scm, gnu/packages/ruby.scm,
gnu/packages/rust.scm, gnu/packages/scheme.scm,
gnu/packages/serialization.scm, gnu/packages/shells.scm,
gnu/packages/ssh.scm, gnu/packages/suckless.scm, gnu/packages/tbb.scm,
gnu/packages/telephony.scm, gnu/packages/text-editors.scm,
gnu/packages/textutils.scm, gnu/packages/time.scm, gnu/packages/tls.scm,
gnu/packages/tor.scm, gnu/packages/version-control.scm,
gnu/packages/video.scm, gnu/packages/vim.scm, gnu/packages/web.scm,
gnu/packages/wm.scm, gnu/packages/xdisorg.scm, gnu/packages/xfce.scm,
gnu/packages/xml.scm, gnu/packages/xorg.scm, gnu/services/certbot.scm,
gnu/services/desktop.scm, gnu/services/version-control.scm,
gnu/services/web.scm, guix/import/hackage.scm, guix/licenses.scm: Likewise.

Signed-off-by: Efraim Flashner <efraim@flashner.co.il>

doc: Specify the branch name in the title of a patch.

* doc/contributing.texi (Submitting Patches): Add branch name in the
title of a patch if different than master.

guix graph: Add '--path'.

* guix/scripts/graph.scm (display-path): New procedure.
(%options, show-help): Add '--path'.
(guix-graph): Handle it.
* tests/guix-graph.sh: Add tests.
* doc/guix.texi (Invoking guix graph): Document it.
(Invoking guix size): Mention it.

doc: Mention xdot.

* doc/guix.texi (Invoking guix graph): Mention xdot.  Remove a couple of
"| dot -Tpdf" in examples and add "| xdot".
(Invoking guix system): Likewise.
(Preparing to Use the Bootstrap Binaries): Likewise.

Merge branch 'core-updates'

doc: Use @option for command-line options

* doc/guix.texi (Invoking guix system): Use @option instead of @code.

guix system: 'docker-image' honors '--network'.

* gnu/system/vm.scm (system-docker-image): Add #:shared-network? and
pass it to 'containerized-operating-system'.
(qemu-image):
* guix/scripts/system.scm (system-derivation-for-action): Pass
 #:shared-network? to 'system-docker-image'.
* doc/guix.texi (Invoking guix system): Document it.

doc: Tiny markup fix.

* doc/guix.texi (Substitute Authentication): Use @samp instead of @code for
pseudo-code.

doc: Remove markup for external package names.

* doc/guix.texi (Invoking guix import): Remove markup, which is not warranted
here.

doc: Use @file instead of @code also for file extensions.

* doc/guix.texi (Defining Packages):
(Build Systems):
(Derivations):
(Invoking guix import):
(Printing Services):
(Installing Debugging Files):
(Preparing to Use the Bootstrap Binaries): Use @file instead of @code.

doc: Use @env for environment variables.

* doc/guix.texi (Binary Installation):
(Build Environment Setup):
(Invoking guix-daemon):
(Application Setup):
(After System Installation):
(Invoking guix package):
(Proxy Settings):
(Invoking guix environment):
(Packages for C Development):
(Package Modules):
(Build Systems):
(The Store):
(Common Build Options):
(Invoking guix download):
(Invoking guix refresh):
(Using the Configuration System):
(Locales):
(Base Services):
(Networking Services):
(Sound Services):
(Continuous Integration):
(PAM Mount Service):
(X.509 Certificates): Use @env instead of @code for environment variables.

doc: Use @option instead of @code.

* doc/guix.texi (Binary Installation):
(Requirements):
(Build Environment Setup):
(Invoking guix-daemon):
(Application Setup):
(Invoking guix package):
(Substitute Server Authorization):
(Substitution Failure):
(Invoking guix gc):
(Invoking guix pull):
(Invoking guix archive):
(Invoking guix environment):
(Invoking guix pack):
(Defining Packages):
(Build Systems):
(The Store):
(Invoking guix build):
(Common Build Options):
(Package Transformation Options):
(Additional Build Options):
(Debugging Build Failures):
(Invoking guix edit):
(Invoking guix import):
(Invoking guix refresh):
(Invoking guix lint):
(Invoking guix publish):
(Invoking guix challenge):
(Base Services):
(Virtualization Services):
(Initial RAM Disk):
(Invoking guix system):
(Preparing to Use the Bootstrap Binaries):
(Porting): Use @option instead of @code for command-line options.

doc: Fix typo in container example.

* doc/guix.texi (Invoking `guix environment'): Fix sll -> ssl typo.

doc: Add container example to run a web browser.

* doc/guix.texi (Invoking `guix environment'): Add paragraph and example to
  run Eolie in a guix environment container.  Add `container' cindex for the
  first container example, and the `certificates' cindex for the web browser
  example.