ghc-cabal mishandles relative paths in arguments
Just making a record of this one, don't expect it to get fixed in a hurry
ghc-cabal chdirs into the source directory when it runs, because cabal wants to run there. Unfortunately this means relative paths in the arguments are treated as relative to the cabal file, rather than the directory where ghc-cabal was invoked. This is notably an issue for --package-db, which currently requires an absolute path in order to avoid this issue.
(This appears to be the last thing in ghc which needs an absolute path; when it's gone, a lot of things become simpler)