This is so the new JSON library we're using doesn't break things. :)
Note also the "8.1" added to the end of the vcvars line in the batch
file, so the correct SDK is selected.
Without it, when both MSVC 2015 & MSVC 2017 are installed, the MSVC
2015 installation (by default) will be unable to find rc.exe.
All the new committed files are the same as the current files, but have "_new" suffix so they can be tested without breaking the current build system. Once tested, the old files can be removed and the new ones renamed.
See issue #1630.
Justin Clift