chore(3p/lisp): import mime4cl source tarball

Used http://wcp.sdf-eu.org/software/mime4cl-20150207T211851.tbz (sha256
5a914669bba7561efe59a4fd0817204c07ad2add98b03ae206ef185ac04affb3).
Importing seems sensible since there's no upstream repo nor has their
been a release since 2015.

This is just an import commit, so the changes made to make it build are
more discoverable as their own commit.

Change-Id: I2ff28c3c7433abdf7857204bc89eaf9edc0b1cbc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3378
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

third_party/lisp/mime4cl/test/package.lisp

@@ -0,0 +1,28 @@
+;;;  package.lisp --- package description for the regression tests
+
+;;;  Copyright (C) 2006, 2009 by Walter C. Pelissero
+
+;;;  Author: Walter C. Pelissero <walter@pelissero.de>
+;;;  Project: mime4cl
+
+#+cmu (ext:file-comment "$Module: package.lisp $")
+
+;;; This library is free software; you can redistribute it and/or
+;;; modify it under the terms of the GNU Lesser General Public License
+;;; as published by the Free Software Foundation; either version 2.1
+;;; of the License, or (at your option) any later version.
+;;; This library 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
+;;; Lesser General Public License for more details.
+;;; You should have received a copy of the GNU Lesser General Public
+;;; License along with this library; if not, write to the Free
+;;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+;;; 02111-1307 USA
+
+(cl:in-package :common-lisp)
+
+(defpackage :mime4cl-tests
+  (:use :common-lisp
+	:rtest :mime4cl)
+  (:export))