We should provide nightlies for a i686-pc-windows-msvc host compiler (much in the same way we have a x86_64-pc-windows-msvc host compiler). Unfortunately there is currently a bug in LLVM preventing us from doing so, so the bootstrap aborts at libsyntax because of this bug: https://llvm.org/bugs/show_bug.cgi?id=23957

Build system support is being added in #26601, but it's largely untested because a compiler could never be produced!