Sergei Trofimovich authored Sep 02, 2016 and Ben Gamari committed Sep 19, 2016

The following command fails as:
    $ ./configure --prefix=/usr \
        --build=x86_64-pc-linux-gnu \
        --host=x86_64-pc-linux-gnu \
        --target=x86_64-pc-linux-gnu
    configure: error:
    You've selected:

      BUILD:  x86_64-unknown-linux
      HOST:   x86_64-unknown-linux
      TARGET: x86_64-unknown-linux

    BUILD must equal HOST;

18f06878

 changed native
configure $build/$host/$target checks to ghc-mangled ones,
but not completely.

Signed-off-by: Sergei Trofimovich <siarheit@google.com>

Reviewers: rwbarton, erikd, austin, hvr, bgamari, Phyx

Reviewed By: Phyx

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2508

GHC Trac Issues: #12487

(cherry picked from commit 0cc3931b)