Squashed 'site_scons/' changes from 2aad345..ea4558b

ea4558b Refine regex used to get clang version and call default without version

git-subtree-dir: site_scons
git-subtree-split: ea4558b35f952ac9a5e60fc118c6cb900d251d3e
Merge commit '6489c6b8195ec2682a7fac7f4133418629eee11d'