Support `stack setup` on Linux with libtinfo6

[borsboom]

Most "bleeding edge" distros (e.g. Arch (#257) and Gentoo) have already upgraded to ncurses6, and now Fedora 24 (#2300) has been released that uses it as well. With these distros, you'll see an error like this when you run stack setup:

/home/user/.stack/programs/x86_64-linux/ghc-7.10.3/lib/ghc-7.10.3/bin/ghc-pkg: error while loading shared libraries: libtinfo.so.5: cannot open shared object file: No such file or directory

Unfortunately, there are no official GHC bindists for stack setup to use that support it. Provisional plan:

• Build our own GHC bindists with libtinfo6, for 64bit and 32bit
• Teach Stack to detect when it is on a system with libtinfo6 and select the appropriate bindist from setup-info (similarly to how we detect libgmp3 and chose a centos6 bindist).

[borsboom]

Question: which GHC versions should we build bindists for? At least ghc-8.0.1 and 7.10.3, obviously (for current LTS 6 and nightly snapshots). Probably 7.8.4 (for older LTS snapshots), and perhaps also 7.10.2 (used by LTS 3, although Stack can be easily configured to use GHC 7.10.3 in this case). We've never had an LTS snapshot use GHC 7.10.1, I don't think we need to support it.

[borsboom]

I've built a GHC 7.10.3 64-bit bindist to try out. For anyone running into this problem, please try putting this in your ~/.stack/config.yaml:

setup-info:
  ghc:
    linux64:
      7.10.3:
        url: "https://github.com/commercialhaskell/ghc/releases/download/ghc-7.10.3-release/ghc-7.10.3-x86_64-fedora24-linux.tar.bz2"
        content-length: 135082273
        sha1: cdd3ae99725218bb994936f5ab14fdb69307216e

And then re-run stack setup. I've tried it on Fedora 24, seems to work, but I'm interested in both positive and negative reports with other distributions. Let me know how it goes!

[borsboom]

Also tried it on Arch Linux, but unfortunately it didn't work out-of-the-box. See #257 (comment).

[crocket]

I think it's easier to statically link libtinfo with GHC. I don't know if it would make things more difficult in the future.

[borsboom]

With 05ba87e (to be included with stack-1.2.0), stack setup gains the ability to detect systems with libtinfo.so.6 and download an appropriate GHC bindist. I've built 64-bit bindists on Fedora 24 for GHC 8.0.1, 7.10.3, 7.10.2, and 7.8.4 (all versions that have Stackage LTS snapshots). Since I'm having trouble finding 32-bit Fedora 24 images, I haven't built any 32-bit bindists, but I'd be happy to accept them from contributors (see GHC build instructions).

Please re-open this issue if you run into any trouble.