* guix/zlib.scm, tests/zlib.scm: New files. * Makefile.am (MODULES): Add guix/zlib.scm. (SCM_TESTS): Add tests/zlib.scm. * m4/guix.m4 (GUIX_LIBGCRYPT_LIBDIR): New macro. * configure.ac (LIBGCRYPT_LIBDIR): Use it. Define and substitute 'LIBZ'. * guix/config.scm.in (%libz): New variable.