vcvarsall.bat needs to be called like soc vcvarsall.bat [arch] [platform_type] [winsdk_version] [-vcvars_ver=vc_version] [-vcvars_spectre_libs=spectre_mode]
arch is one of (as shown above) x86
x64
x64_x86
x86_x64 winsdk_version is 10.0.10240.0 (10240 being the build number) see Windows versions)
8.1 (for the Windows 8.1 SDK) -vcvars_ver apparently specifies the VC tool set: 14.0 for VC++ 2015
14.1x
14.1x.yyyy
spectre_mode is either none
spectre vcvarsall.bat relate to VsDevCmd.bat?