Squashed 'site_scons/' changes from 93bb5a6..e61b6fd

e61b6fd Change clang-darwin to darwin-clang for boost

git-subtree-dir: site_scons
git-subtree-split: e61b6fd950fc3843e6265eec98ecc59e1cc4a57c
Merge commit 'cd27947eb5b075c565deed96b5c1d5cfe6074069'