[boost] Build breaking changes

Hello, I've just noted that building Boost from master stopped working: [00:16:51] b2.exe -j4 toolset=gcc --layout=system variant=release architecture=x86 link=static --with-program_options --with-filesystem --with-system --with-test --with-atomic --with-thread --with-timer --with-date_time --with-chrono --with-regex --with-random --with-context stage [00:16:52] Performing configuration checks [00:16:52] [00:16:52] - default address-model : 32-bit [00:16:53] - default architecture : x86 [00:16:53] - symlinks supported : yes (cached) [00:16:54] - C++11 mutex : yes [00:16:55] - has_icu builds : no [00:16:55] - BOOST_COMP_GNUC >= 4.3.0 : yes [00:16:55] - C++11 mutex : no [00:16:56] - has_icu builds : no [00:16:56] - BOOST_COMP_GNUC >= 4.3.0 : no [00:16:56] error: Name clash for 'libboost_atomic.a' [00:16:56] error: [00:16:56] error: Tried to build the target twice, with property sets having [00:16:56] error: these incompatible properties: [00:16:56] error: [00:16:56] error: - <address-model>64 [00:16:56] error: - <address-model>32 [00:16:56] error: [00:16:56] error: Please make sure to have consistent requirements for these [00:16:56] error: properties everywhere in your project, especially for install [00:16:56] error: targets. [00:16:56] [00:16:56] Command exited with code 1 Previously this build command worked fine. Full log available at https://ci.appveyor.com/project/apolukhin/boost-cookbook/branch/second_editi... Is this an intended breaking change?