build: don't add libraries when --enable-static

Currently when building with --enabled-static the cctest target will
include libraries to be linked regardless. This commit adds a condition
to only add the libraries when dynamically linking.

PR-URL: https://github.com/nodejs/node/pull/14837
Fixes: https://github.com/nodejs/node/issues/13500


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>