VS: Recognize VS/LLVM toolset names as Clang

Update the toolset name matching added by commit v3.6.0-rc1~279^2~10
(VS: in Clang/C2 toolset, setup correct compiler settings, 2016-02-18)
to match VS/LLVM toolset names too.
Status Job ID Name Coverage
  External
passed kwrobot-branch-check