Add configure support for ppc64el

Add configure support for ppc64el

This patch was originally introduced [1] and rebased [2] in Ubuntu Trusty [3].

Some chunks were changed/removed on Debian:
  - The DPKG_ARCH / UNAME_MACHINE mapping is actually Debian-specific, and done
    in another patch; so this chunk is now there.
  - The 'PLATFORM=qws/linux-*-g++' setting is not required; ppc64el builds fine
    with the default 'linux-generic-g++'  (the difference to the previously set
    'linux-x86_64-g++' is just '-m64', which is default/only-option on ppc64el).

[1] http://launchpadlibrarian.net/159898800/qt4-x11_4:4.8.4+dfsg-0ubuntu20_4:4.8.4+dfsg-0ubuntu21.diff.gz
[2] http://launchpadlibrarian.net/162331250/qt4-x11_4:4.8.4+dfsg-0ubuntu22_4:4.8.5+git192-g085f851+dfsg-2ubuntu1.diff.gz
[3] https://launchpad.net/ubuntu/+source/qt4-x11/+changelog

Gbp-Pq: Name ppc64el_configure_support.patch