Squashed 'site_scons/' changes from e61b6fd..b7fdfc5

b7fdfc5 Reset clang-darwin toolset name and print bjam command

git-subtree-dir: site_scons
git-subtree-split: b7fdfc5fd5eb80821b65117338e47a7d93ec09d0
Merge commit 'd6ce8347f3b0a5afb9edbb34b915a88034b2074a'