Hadrian: support extra libraries + OSX rpath
This fixes some of the issues that surfaced when trying to build
dynamic GHC on OSX. Unfortunately, due some other libffi
issues, this doesn't completely fix dynamic builds on OSX.
- Use 'extra-libraries' from .cabal files instead of hardcoding which packages need which extra libs. Also add support for 'extra-lib-dirs'.
- Make sure Hadrian looks in the right places to support both plain '<pkg>.buildinfo' and '<pkg>.buildinfo.in' files.
- Make the '-rpath' support more robust across OS's (it previously didn't work on OSX and possibly windows either).
Reviewers: angerman, alpmestan, adamse, DavidEichmann, bgamari, Phyx
Subscribers: rwbarton, carter
GHC Trac Issues: Trac #15990
Differential Revision: https://phabricator.haskell.org/D5409