Takenobu Tani authored Apr 13, 2019 and Ben Gamari committed Jun 12, 2019

In order to use the `:doc` command in ghci, it is necessary
to compile for core libraries with `-haddock` option.

Especially, the `-haddock` option is essential for release building.

Note:
  * The `-haddock` option may affect compile time and binary size.
  * But hadrian has already set `-haddock` as the default.
  * This patch affects the make-based building.

This patch has been split from !532.

(cherry picked from commit 33e37d06)