Even though the case is justified, we shouldn't render whole setups unsupported because of that, as running as root, while discouraged, does not directly affect the program stability.
This is especially true on Windows boxes where there is a lot of setups running with administrators by default and users are not even aware of that, I don't have a good fix for them (apart from reinstallation), and because I do not, I should not expect from them to supply cmd-line arg they don't even understand why.
Skipping a 20 KB stub in OS-specific non-windows builds and omitting a few very fast if checks isn't worth the code quality degradation that involves all of the ifdef options.
ifdefs should be reserved for stuff that either doesn't compile whatsoever in some specific configurations (NETFRAMEWORK), or is required to make logical decisions based on the compiler input (e.g. DEBUG for detecting debugging builds or ASF_VARIANT_* for hardcoding the platform identifier to use for auto-updates)
In all other situations, we should use OperatingSystem if condition, even if it's equal to hitting them on the platforms that are unlikely to hit them.
And I say unlikely, because nothing stops me from downloading a win-x64 build and running it like a generic one on windows, what you gonna do?