If libtinfo5 isn't installed, then installation fails with a message like this:
/home/ubuntu/.ghcup/ghc/8.6.5/lib/ghc-8.6.5/bin/ghc-pkg: error while loading shared libraries: libtinfo.so.5: cannot open shared object file: No such file or directory
If xz-utils isn't installed, then installation fails with a message like this:
Following commands are required, but missing, please install: xz
* the bindists are not official
* we have to allow curl to follow redirects, because github
hosts on AWS
* bindists are built without haddock support, so those symlinks
must be conditional for now, see
https://github.com/redneb/ghc-alt-libc/issues/5
