Summary: it was a lot more trouble than I expected.
There are three main things I did to stop
npm install ffi from failing after an “MSB8020” error about the v100 Platform Tools not being available:
- I updated npm’s bundled node-gyp, although I suspect this made no difference.
- I repaired my installation of Visual Studio 2013 Express to clean up from my previous attempts to install Visual Studio 2010 at the same time.
- I failed to install the wrong Windows 7 SDK, failed to uninstall it, succeeded in uninstalling it, and installed the right version of the Windows 7 SDK, as linked from the Mozilla Developer Network documentation about Windows SDK versions.