message: boost: compile for macOS 10.7
  Currently we have warnings about mixing compilation for 10.12 and
  linking for 10.7.
diff: @@ -10,6 +10,8 @@ import sys
  from itertools import chain
  +MACOSX_DEPLOYMENT_TARGET = '10.7'
  +
  archs = None
  athena = None
  aws = None
  @@ -1060,7 +1062,8 @@ using python : %(python_version)s : %(python_prefix)s/%(python_bin)s : %(python_
  elif cxx_toolkit.os is drake.os.macos and \
  cxx_toolkit.kind == drake.cxx.GccToolkit.Kind.clang:
  self.__command += [
  - 'cxxflags=-stdlib=libc++ -std=c++11',
  + 'cxxflags=-stdlib=libc++ -std=c++11 -mmacosx-version-min={}'
  + .format(MACOSX_DEPLOYMENT_TARGET),
  'linkflags=-stdlib=libc++ -std=c++11',
  '--layout=infinit_osx',
  ]
  