Path lists on windows should always be separated by semicolons, not colons. Reuse llvm::sys::EnvPathSeparator for this purpose (as that's also a path list that is separated in the same way).
Alternatively, this could just be a local ifdef _WIN32 in this function, or should we generalize the existing EnvPathSeparator to e.g. a llvm::sys::path::PathListSeparator?
Does this change need a test? I guess we could add a separate file with "REQUIRES: system-windows" and check if the output does contain a semicolon, but I'm not sure how meaningful that is, especially as the default list printed only contains one single path element.
This was noted within Qt (and worked around with a creative regex) at https://codereview.qt-project.org/247331.