* tests/lzlib.scm: Use test-assert* for all test cases, so that there are no failures if lzlib is unavailable.
* guix/lzlib.scm (lzwrite!, make-lzip-input-port/compressed): New procedures. * tests/lzlib.scm ("make-lzip-input-port/compressed"): New test. * guix/tests.scm (%seed): Export.
* guix/lzlib.scm, tests/lzlib.scm: New files. * Makefile.am (MODULES): Add guix/lzlib.scm. (SCM_TESTS): Add tests/lzlib.scm. * m4/guix.m4 (GUIX_LIBLZ_LIBDIR): New macro. * configure.ac (LIBLZ_LIBDIR): Use it. Define and substitute 'LIBLZ'. * guix/config.scm.in (%liblz): New variable. * guix/self.scm (make-config.scm): Add TODO comment. Co-authored-by: Ludovic Courtès <ludo@gnu.org>