You have built Boost on FreeBSD 4, which comes with the GCC 2.95.4
compiler suite.

Since the standard template library of g++ 2.95.4 is not compatible
with this version of Boost, the library has been built against the
STLport library (devel/stlport).

In order for your own code to link properly, you have to built it
with STLport also. You are advised to use the following compiler
and linker options:

Compiler options (be sure to append any additional options after these!)
   -nostdinc -I%%LOCALBASE%%/include/stlport -I/usr/include

Linker options:
   -L%%LOCALBASE%%/lib -lstlport_gcc