Squashed 'site_scons/' changes from 3e485b2..f062937

f062937 Enable multi-toolchain support and add clang toolchain

git-subtree-dir: site_scons
git-subtree-split: f0629375143f936479b45cc0dc33398a1a24eb0f
Merge commit 'c44cb6153b90e9df9718d5b924bdb9f49a6be1c6'