[cmake] Use Boost_THREADAPI to select the flavor of the thread API we want to use on windows

Summary: This is the proper way to do it. Also updated the depends build to make sure the right dependencies are included.

Test Plan: Build with ninja on linux + cross compilation on windows 32 and 64.

Reviewers: #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: schancel, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1358