Hey there, I maintain the LyX port on FreeBSD, and was recently contacted by a user who was not able to built LyX with GCC 4.5 due to autoconf trying to use gcc instead of g++ to build the source code used to link to boost (LyX is built with --without-included-boost).
The patch below should fix the problem: AC_CHECK_LIB uses a C compiler, so we need to manually set the language to C++ and call AC_LINK_IFELSE.
Index: config/lyxinclude.m4 =================================================================== --- config/lyxinclude.m4 (revision 39661) +++ config/lyxinclude.m4 (working copy) @@ -321,8 +321,17 @@ AM_CONDITIONAL(USE_INCLUDED_BOOST, test x$lyx_cv_with_included_boost = xyes) AC_MSG_RESULT([$lyx_cv_with_included_boost]) if test x$lyx_cv_with_included_boost != xyes ; then - AC_CHECK_LIB(boost_signals, main, [lyx_boost_underscore=yes], [], [-lm]) - AC_CHECK_LIB(boost_signals-mt, main, [lyx_boost_underscore_mt=yes], [], [-lm $LIBTHREAD]) + AC_LANG_PUSH(C++) + SAVED_LDFLAGS=$LDFLAGS + + LDFLAGS="$SAVED_LDFLAGS -lboost_signals -lm" + AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <boost/signal.hpp>], [boost::signal<void ()> s;])], [lyx_boost_underscore=yes], []) + LDFLAGS="$SAVED_LDFLAGS -lboost_signals-mt -lm $LIBTHREAD" + AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <boost/signal.hpp>], [boost::signal<void ()> s;])], [lyx_boost_underscore_mt=yes], []) + + LDFLAGS=$SAVED_LDFLAGS + AC_LANG_POP(C++) + if test x$lyx_boost_underscore_mt = xyes ; then BOOST_MT="-mt" else
