Centralize the definition for GHC's libdir on Windows
The location of GHC libraries on Windows is currently something like
$bindir/../lib (because the whole distribution can be put anywhere on the filesystem, there are no absolute paths), but this information is hard-coded in multiple places instead of being defined in one place. To be clear, I mean only the relative path (
../lib); the base still needs to be determined at runtime.
I assume that tools that can rely on
ghc --info (or equivalent) already do that. If there are any that don't, they should be fixed regardless. The build system, ghc, ghc-cabal, ghc-pkg, hsc2hs, haddock... should all be able to get the relative path from