Support Hadrian bindists
Alpine bindist releases (e.g. ghc-8.10.1-x86_64-alpine3.10-linux-integer-simple) are now generated via GitLab CI using the Hadrian build system.
GHCup currently relies on bin/ghc being a symlink to a versioned ghc binary (e.g. ghc-8.10.1) but this is not the case when using a Hadrian bindist:
It looks like GHCup is doing this to only find executable without a version suffix. Luckily Hadrian builds don't have version suffixes in the bin directory, so we should be able to remove the filter completely if there's no symlink: