As outlined in #15925, hadrian bindists had not made a clear choice with
respect to relocatable GHCs and wrapper scripts. This commit implements
the policy described in the ticket. That is:

- the bindists ship {bin, lib} as they are, modulo the addition of
  haddock from stage2/bin
- we now _always_ generate wrapper scripts for all the programs that
  are in the bindist's bin/ directory

The idea being that anyone on Linux/Windows/OS X can just unpack
the binary distribution anywhere and start using bin/ghc, while the
installation process systematicaly generates wrapper scripts.

Test Plan: hadrian/build.sh binary-dist ; cd
_build/bindist/ghc-X.Y.Z-arch/; configure --prefix=/tmp/foo && make
install

Reviewers: snowleopard, bgamari, angerman

Reviewed By: snowleopard, bgamari, angerman

Subscribers: rwbarton, carter

GHC Trac Issues: #15925

Differential Revision: https://phabricator.haskell.org/D5371