allow to specify libgmp location, by using --with-libgmp-prefix, by default current prefix is also searched allow to specify libb2 location, by using --with-bz2-prefix, by default current prefix is also searched locating gmp and bz2 works by default on OpenBSD (bb #301) move local m4 macros to m4/ import lib-link.m4 and dependent files quoting for autoconf macros (bb #452)