Import some shellquote utility functions from qmake.

Will be used by future patches.

Change-Id: I20bc0cdcbf8bde8d351e3fce30d3e15f1cb444e8
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>