The most complex problems were from dealing with switches reverted in
the meantime (gcc5, gmp6, ncurses6).
It's likely that darwin is (still) broken nontrivially.
... because cc-wrapper is meant to propagate man pages into user envs,
and info pages are rather large.
Also replace the duplicate g++ and gcc man1 pages by a symlink.
This reverts commits cb7c053383ff76a454484992b3a6d6a2f1530c15,
ebda45e6b9db3225c30a998b2624d90b0c08edb4,
4a495cfbab2b3ab9ae8219ef1812c766bf27b01e because they broke Nixpkgs
evaluation.
http://hydra.nixos.org/build/24813270
