[boost] How to build Boost with VS15

Hi, How does one build Boost (1.62) with VS15 (Preview 4)? I know it's not officially supported.. C:\VC\boost>bootstrap.bat Building Boost.Build engine 'cl' is not recognized as an internal or external command, operable program or batch file. Failed to build Boost.Build engine. Please consult bootstrap.log for further diagnostics. -- Olaf