* Adjust CI to work with modular branches.
* Add modular build setup.
* Add modular build setup.
* Avoid complexities of shared libs for CI.
* Fix filsystem lib refs.
* Remove redundant build//install target.
* Fix reference to build in CI as a way to dist install.
* Build the dist target for tools by default.
* Rework BOOST_BRANCH value to avoid modular branch name in the logic.
* Use imperative declarations of explicit targets per @pdimov's preference.
* Remove temp link=static that crept in for CI build.
* Add requires-b2 check to top-level build file.
* Bump B2 require to 5.2
* Undo modular CI testing fork changes.
* Need to explicitly install boostdep for this test.
