build-system/mozilla: New build system.

* guix/build-system/mozilla.scm
  (lower-mozilla): New procedure.
  (mozilla-build-system): New variable.
* Makefile.am (MODULES): Add it.
* doc/guix.texi (Build Systems): Document it.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

Makefile.am

@@ -140,6 +140,7 @@ MODULES =					\
   guix/build-system/font.scm			\
   guix/build-system/go.scm			\
   guix/build-system/meson.scm			\
+  guix/build-system/mozilla.scm			\
   guix/build-system/minify.scm			\
   guix/build-system/minetest.scm		\
   guix/build-system/asdf.scm			\

doc/guix.texi

@@ -8000,6 +8000,15 @@ directory, the parameter @code{#:javascript-files} can be used to
 specify a list of file names to feed to the minifier.
 @end defvr
 
+@defvr {Scheme Variable} mozilla-build-system
+This variable is exported by @code{(guix build-system mozilla)}.  It
+sets the @code{--target} and @code{--host} configuration flags to what
+software developed by Mozilla expects -- due to historical reasons,
+Mozilla software expects @code{--host} to be the system that is
+cross-compiled from and @code{--target} to be the system that is
+cross-compiled to, contrary to the standard Autotools conventions.
+@end defvr
+
 @defvr {Scheme Variable} ocaml-build-system
 This variable is exported by @code{(guix build-system ocaml)}.  It implements
 a build procedure for @uref{https://ocaml.org, OCaml} packages, which consists

guix/build-system/mozilla.scm

@@ -0,0 +1,52 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build-system mozilla)
+  #:use-module (guix build-system gnu)
+  #:use-module (guix build-system)
+  #:use-module (guix utils)
+  #:export (mozilla-build-system))
+
+;;
+;; Build procedure for packages using Autotools with the Mozillian conventions
+;; for --target, --host and --build, which are different from the GNU
+;; conventions.
+;;
+;; Code:
+
+(define* (lower-mozilla name #:key system target #:allow-other-keys
+                        #:rest arguments)
+  (define lower (build-system-lower gnu-build-system))
+  (if target
+      (apply lower
+             (substitute-keyword-arguments arguments
+               ;; Override --target and --host to what Mozillian configure
+               ;; scripts expect.
+               ((#:configure-flags configure-flags ''())
+                `(cons* ,(string-append "--target=" target)
+                        ,(string-append "--host=" (nix-system->gnu-triplet system))
+                        ,configure-flags))))
+      (apply lower name arguments))) ; not cross-compiling
+
+(define mozilla-build-system
+  (build-system
+    (name 'mozilla)
+    (description "The build system for Mozilla software using the Autotools")
+    (lower lower-mozilla)))
+
+;;; mozilla.scm ends here