cmake-gui: CMAKE_GENERATOR_PLATFORM environment variable isn't respected
I've got a project that needs to be built with MSVC 2017 x64. I've set the CMAKE_GENERATOR environment variable to "Visual Studio 15 2017", and CMAKE_GENERATOR_PLATFORM to "x64". On the command line, this is sufficient to get the correct generator and platform. With cmake gui, the generator again defaults to "Visual Studio 15 2017" (which is nice given that I've got 2019 installed as well, so that seems to work), but the architecture still defaults to blank, resulting in Win32 getting used.
I think the simplest fix would be to just default that dropdown to the entry that matches CMAKE_GENERATOR_PLATFORM (if available/valid), and blank otherwise. If that works for you guys, I can probably fix this myself and open a PR.