ghc{843,861}: clone linux-gnu targets so musl variants are available

Fixes build with "muslpi" (armv6l-unknown-linux-musleabihf).

This was done via patch at first but it wouldn't apply to both at once,
and it's probably best to stick to just having musl clones for now
(instead of patching 8.6.1 targets into 8.4.3 and hoping that's okay).