bcp namespace aliasing broken, impacts package providers, shared libraries unusable since 1.69

From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2019-05-24 08:58:18

Hi,

I'd like to point out that bcp namespace aliasing has been broken for
quite a while, which impacts package providers of Boost which choose
to package it with a versioned namespace.
We should try to fix to enable more people to upgrade.

The bug has been reported March 2018 on trac
https://svn.boost.org/trac10/ticket/13460
Then again by me this week on github https://github.com/boostorg/bcp/issues/4

Things have been made worse since 1.69 because libraries now build
with visibility hidden by default, which means that with this bug
symbols don't get exported and nothing links.

Also I would argue that this set-up should be tested as part of the
release validation process.
The boost build system is arcane enough that we don't need a pretty
standard build configuration to be subtly broken for more than a year.

Could we try to address this before 1.71?