Configure: fixed build with --with-stream.

Configure: fixed build with --with-stream.

Some combinations of options might cause the builds with the
--with-stream option to break due to invalid value of the
STREAM_INCS make variable, e.g.

auto/configure \
    --with-stream \
    --with-http_perl_module=dynamic \
    --without-http_memcached_module \
    --without-http_empty_gif_module \
    --without-http_browser_module \
    --without-http_upstream_hash_module \
    --without-http_upstream_ip_hash_module \
    --without-http_upstream_least_conn_module \
    --without-http_upstream_keepalive_module \
    --without-http_upstream_zone_module \

Explicit initialization of ngx_module_libs and ngx_module_link
matches what we already do when processing mail modules, and
is also required after the next change.