boost: reference patch with issue reports.
boost: trunk now on github with submodules.

* Also remove legacy rpath handling logic, which is taken care of by
  install_name_tool.
boost: fix C++11 flags for trunk.

* Trunk now use "-x" flag to control which language to use, for instance
  "clang++ -x c" will be used to compile C code, while Homebrew will
  still think it is invoking the C++ compiler. It is easier to just set
  cxxflags and linkflags.