[boost] [Config][auto_link] BOOST_LIB_TOOLSET override does not work as intended when multiple libraries are used

For example, if BOOST_LIB_TOOLSET is defined as "iw90" and both thread and signals libraries are used in a cpp file, compiler prints out the following: Linking to lib file: libboost_thread-iw90-mt-s-1_33.lib Linking to lib file: libboost_signals-iw-mt-s-1_33.lib The problem is caused by BOOST_LIB_TOOLSET being undefined at the end of auto_link.hpp. The second time auto_link.hpp is included (it has no include guards and is meant to be included multiple times) BOOST_LIB_TOOLSET is not defined anymore and a default value will be assigned. Does it really need to be undef'ed? Thanks, Sean