[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