rustc: add backport build chain for firefox source

helpers/make-rustc

+#!/bin/sh
+#
+#    Copyright (C) 2022  Luis Guzmán <ark@switnet.org>
+#
+#    This program 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 2 of the License, or
+#    (at your option) any later version.
+#
+#    This program 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 this program; if not, write to the Free Software
+#    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+#
+
+
+##
+# rustc 1.62 version to start build chain for rust 1.63/cargo 0.64
+#
+VERSION=0
+EXTERNAL='deb-src http://ppa.launchpadcontent.net/schopin/rustc-1.62/ubuntu $UPSTREAM main'
+REPOKEY=F8B13AAE84229B75
+BACKPORTS=true
+. ./config
+
+
+changelog "Import as dependency of newer abrowser (deb) dependencies."
+compile