Squashed 'site_scons/' changes from b7fdfc5..bc3d0e2

bc3d0e2 Remove version from clang-darwin toolset name

git-subtree-dir: site_scons
git-subtree-split: bc3d0e2ffb44dea2b3bd3756776eaad2cf654e1c
Merge commit '97ef230f2fa1b1c6b07f06d4f8641d5ab9558b16'