Reorder checks for libraries to allow ./configure LDFLAGS=-static.

OpenSSL depends on libdl and libz. When linking dynamically, libcrypto will
automatically link with the other two libraries.  However, when linking
statically, these libraries need to be specified explicitly while linking.  By
moving the autoconf checks for libdl and libz before those for libcrypto, we
ensure the latter test will be done with the proper libraries.