Build fails with the usual > /var/tmp/portage/dev-lang/ghc-8.0.2/work/usr/lib/ghc-8.0.2/bin/ghc-pkg: No such file or directory because the binaries used for bootstrapping are not fully statically linked and require glibc. Later unstable versions have the same problem.
My understanding is it is not enough to have static ghc to be able to build ghc on foreign libc. ghc comes with it's standard library (base, unix, rts) that use libc definitions gathered at ghc compile time. I expect them to be unlinkable on foreign libc.
*** Bug 712334 has been marked as a duplicate of this bug. ***
*** Bug 712338 has been marked as a duplicate of this bug. ***
Upstream provide binary packages for Alpine Linux 3.10 in GHC 8.10 and 9.0
You can find musl linked haskell bootstrap tarballs here https://github.com/redneb/ghc-alt-libc We should probably look at integrating this with the musl overlay first, and then the main tree.
