ghc-8.8.1 RC1 build no longer detects llc-7.0

Summary

Due to 71aca77c, llvm7.0 is no longer detected on Fedora. I think a change was needed since Debian llvm-7 now ships /usr/bin/llc-7 (compared to Fedora still providing /usr/bin/llc-7.0). The problem is after the above fix I think Debian now detects it's llc-7 correctly but now ghc needs to be patched to detect llc-7.0 on Fedora at least.

BTW It might be better to use Data.Version for LlvmVersion? Then it would be easy to read "7" or "7.0" etc (some distro or system could even have bindir/llc-7.1 or bindir/llc-7.0.1, etc).

(I kind of miss the old --with-llc (and --with-opt) configure options here - were they so bad? 🙂)

Steps to reproduce

Try to configure ghc-8.8.1 RC1 on Fedora ARM (32 or 64 bit) with llvm7.0

Expected behavior

llc-7.0 and opt-7.0 to be detected like for the alpha releases.

Actual behavior

llvm not detected.

Environment

• GHC version used: 8.4.4

Optional:

• Operating System: Fedora
• System Architecture: armv7hl/aarch64

ps I worked around this for now with: https://src.fedoraproject.org/rpms/ghc/blob/694ee07680e4618076b71efa4cc5279984c73e43/f/ghc-8.8-configure-llvm-7.0.patch but we should really detect both llc-7 and llc-7.0 out of the box in my opinion.

I filed a Fedora RFE asking if our llvm7.0 package can provide llc-7 and opt-7 symlinks but there may be other distros shipping llc-7.0. Hopefully in the future Fedora llvm8 package would provide llc-8...