[boost] [Build] Create test with shared library linked against current Boost link-variant

Hi, for a test case for Boost.Serialization  I need to build shared libraries, linked against the current boost library variant (shared or static). How do I do this in Boost.Build? Adding `<link>shared` to the library makes it link against shared boost, but never to static boost. Adding "../build//boost_serialization/<link>static" will be the other way round and fails, if `-fPIC` is not passed, which is not the default. Thanks, Alexander Grund