Generate ';' separated libraries in prl files for CMake.

Generate ';' separated libraries in prl files for CMake.

The generated CMake files need to pass ';' separated libraries to
the IMPORTED_LINK_INTERFACE_LIBRARIES property, otherwise we get errors
such as this:

http://testresults.qt-project.org/ci/QtTools_master_Integration/build_00386/win32-msvc2010_Windows_7/log.txt.gz

(grep for QtCore5.lib.lib)

Rather than a naive and error prone replacement of whitespace, generate
the appropriate ';' separated content directly in the qmake prl file.

Change-Id: I8eb5e233a0318b57ec74b86d910583ff99c29415
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>
Reviewed-by: Brad King <brad.king@kitware.com>
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>