New release.

Boost 1.69.0

From the article:

Notes for non-Windows users
The Boost build system now supports visibilities. If you are building shared libraries, they will use hidden visibility by default. As a result Boost shared libraries become smaller, load faster and have less chances to get a symbol collision.

See Boost.Build visibility and local-visibility for more info.

To disable that feature you can use use a command line ./b2 visibility=global to build...