[cmake] Check if boost::test require static or dynamic linking and act accordingly

Summary: Before, dynamic linking was just assumed, which is not always correct.

Test Plan: Do a cmake build with boost compiled as a static lib.

Reviewers: #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1310