Enable event logging while compiling head.hackage

Creates a wrapper script that Cabal can call for each --make invocation. Adds tracelogs for each compiled unit.

Uses env vars to pass arguments to the wrapper through the cabal call.

Related to ghc#21585 (closed)

requested review from @mpickering and @bgamari

I've been testing this locally with

rm -r ci/run; QUICK=1 GHC=$PWD/ghc-from-artefact/bin/ghc nix run -f ci -c run-ci

(The GHC env var is what the wrapper uses to find the real ghc. Apparently there's no good clue printed to the console if you leave it off, which I'd like to change)

Oops, I misread the line that tars up the artifacts. I didn't notice the -C in front of -C ci/run, so the eventlogs didn't get stored.

added 2 commits

• a69007af - Include eventlogs in artifacts
• 128b7a6a - Make --logging-wrapper optional

Compare with previous version

resolved all threads

Ok, eventlogs are getting put into the artifact now, and they look good after downloading. I'm happy with this patch now.

added 5 commits

• 128b7a6a...673e9fd1 - 2 commits from branch master
• 41fdf917 - Enable event logging while compiling head.hackage
• 72ef56e4 - Include eventlogs in artifacts
• 411d022d - Make --logging-wrapper optional

Compare with previous version

I checked the eventlogs and they look decent! Just one comment about the ghc-pkg stuff.

resolved all threads

added 11 commits

• 411d022d...b3b3b7c3 - 8 commits from branch master
• 400b9dca - Enable event logging while compiling head.hackage
• 67e7ba3a - Include eventlogs in artifacts
• edcbc8c4 - Make --logging-wrapper optional

Compare with previous version

enabled an automatic merge when the pipeline for edcbc8c4 succeeds

merged