document install-dirs

Is it documented how to change $abi and $pkgid for manual installation of haskell packages?

Here is an extract of ~/.cabal/config for reference, regarding these two mentioned variables.

install-dirs global
  -- prefix: /usr/local
  -- bindir: $prefix/bin
  -- libdir: $prefix/lib
  -- libsubdir: $abi/$libname
  -- dynlibdir: $libdir/$abi
  -- libexecdir: $prefix/libexec
  -- libexecsubdir: $abi/$pkgid
  -- datadir: $prefix/share
  -- datasubdir: $abi/$pkgid
  -- docdir: $datadir/doc/$abi/$pkgid
  -- htmldir: $docdir/html
  -- haddockdir: $htmldir
  -- sysconfdir: $prefix/etc

the context of this issue is where GHC is installed into /usr/lib64/ghc-x.x.x

and manually installed packages contain components located in /usr/lib/x86_64-linux-ghc-x.x.x/

the preferred location of all haskell packages' components being under /usr/lib64