rustup fails to open non-existing windows registry path about rustup

[ChrisDenton]

Just to provide some more context, nanoserver is a kind of minimal Windows install that would not be expected to have everything the desktop or full server OS does.

[fruzitent]

running the Rustup CI in the nanoserver image

for msvc toolchain you would have to use the next tier image - servercore (4.5gb), because nanoserver (300mb) does not support running 32-bit executables and .NET Framework used in VS Installer, but i tested gnu toolchain with llvm-mingw, works well.

[rami3l]

Currently we use open_subkey for all Environment related stuff, do in theory replacing that with create_subkey will do.

I'm not sure about the right direction to go though... The most harmless approach would probably be prompting our users to create it on error, but we cannot test this behavior on standard Windows either.

Update: Looks like nothing is stopping me from running the Rustup CI in the nanoserver image, even if it's just for this particular issue. If the perf overhead is negligible, we might even keep it that way.