Update the autotools scripts so that we can copy the Visual Studio
2010 and update items as necessary to obtain the Visual Studio 2017
projects.
Note that the toolset version string format has changed for Visual
Studio 2017, so a custom toolset version string is allowed and used
if specified, otherwise the toolset version string is generated as
we did before.
Note also that Visual Studio 2017 aims to be compatible with Visual
Studio 2015 on the CRT level, so it should be possible to use 2017-
compiled binaries with 2015-compiled binaries without problems.
e3cd67d258