17 Nov
2018
17 Nov
'18
8:12 p.m.
Which version of VS is used by clang-cl.exe is not determined by clang-win.jam, it's decided by clang-cl.exe itself. You could try -fmsc-version=1900, I suppose.
According to https://github.com/llvm-mirror/clang/blob/2bade23358bd718ed8ea2b5f5405ac52e1... the only way to make clang-cl.exe use an older VS installation is to invoke it from the corresponding developer command prompt.