title: OpenBSD boost compiler error
body: <p>I am trying to build boost 1.53 from the ports branch and I get the following errors</p>
  
  <pre><code>error: Duplicate name of actual target: &lt;pstage/lib&gt;libboost_system.a
  error: previous virtual target { common%common.copy-libboost_system.a.STATIC_LIB { gcc%gcc.archive-libboost_system.a.STATIC_LIB { gcc%gcc.compile.c++-error_code.o.OBJ { error_code.cpp.CPP } } } }
  error: created from ./stage-proper
  error: another virtual target { common%common.copy-libboost_system.a.STATIC_LIB { gcc%gcc.archive-libboost_system.a.STATIC_LIB { gcc%gcc.compile.c++-error_code.o.OBJ { error_code.cpp.CPP } } } }
  error: created from ./stage-proper
  error: added properties: &lt;threading&gt;multi
  error: removed properties: &lt;threading&gt;single
  /usr/ports/pobj/boost-1.53.0/boost_1_53_0/tools/build/v2/build/virtual-target.jam:490: in actualize-no-scanner from module object(file-target)@4337
  /usr/ports/pobj/boost-1.53.0/boost_1_53_0/tools/build/v2/build/virtual-target.jam:135: in object(file-target)@4337.actualize from module object(file-target)@4337
  /usr/ports/pobj/boost-1.53.0/boost_1_53_0/tools/build/v2/build-system.jam:749: in load from module build-system
  /usr/ports/pobj/boost-1.53.0/boost_1_53_0/tools/build/v2/kernel/modules.jam:283: in import from module modules
  /usr/ports/pobj/boost-1.53.0/boost_1_53_0/tools/build/v2/kernel/bootstrap.jam:142: in boost-build from module
  /usr/ports/pobj/boost-1.53.0/boost_1_53_0/boost-build.jam:17: in module scope from module
  
  *** Error 1 in . (Makefile:91 'do-build': @cd /usr/ports/pobj/boost-1.53.0/boost_1_53_0 &amp;&amp;  ./bjam -sNO_BZIP2=1  -d+2 -q  -j 1  cflags='-O2 ...)
  *** Error 1 in . (/usr/ports/infrastructure/mk/bsd.port.mk:2619 '/usr/ports/pobj/boost-1.53.0/.build_done')
  *** Error 1 in /usr/ports/devel/boost (/usr/ports/infrastructure/mk/bsd.port.mk:2342 'all')
  </code></pre>
  
  <p>Any ideas ?</p>