Targeting an older version of Windows is "set a define so that the system headers don't expose functions that didn't exist on older Windows". You don't need an old toolchain to target old systems, you ask the newer toolchains to target it.

MS haven't made this work arbitrarily far back, I believe they deprecated targeting Windows XP in one of the more recent toolchains, but that was purely a "not worth supporting" situation.

EDIT: mixed up talking about older & newer