windeployqt: Deploy UNIX/Linux.

Extend platform enumeration by UNIX, determine platform
by running qmake first. Pass platform to relevant functions
(finding binaries, building DLL names, etc).
Use 'ldd' to obtain dependencies of binaries and 'file' to
determine the binary type.
Do ICU/ANGLE handling for Windows only.

Change-Id: I1245c90c0b80fa4039241b556a768a5b28b46771
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>