Fix for Configure to find the path to VC++ redistributables under Visual Studio 2017

Starting with Visual Studio 2017 (15.x), win32utils\Configure can no longer find the path to the 'VC++ 2017 Redistributable' files. To resolve this issue,

add

    # 'VCToolsRedistDir' is available since Visual Studio 2017.
    if ($ENV{"VCToolsRedistDir"}) {
        push(@vcpaths, $ENV{"VCToolsRedistDir"});
    }

after

    if ($ENV{"VCINSTALLDIR"}) {
        push(@vcpaths, File::Spec->catfile($ENV{"VCINSTALLDIR"},
                                           "redist", "1033"));
    }

in win32utils\Configure.

However, this fix does not work for VS 2017 versions 15.5.0, 15.5.1, and 15.5.2, because those versions only ship 'vc_redist.x86.exe' and 'vc_redist.x64.exe'; and 'vcredist_x86.exe' and 'vcredist_x64.exe' are hard-coded in the Windows installer.