iostool: Fix compilation with C++<11

Change-Id: Id026a5f0223dff84568a2c2f3208a3e6eb5410fa
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
Build: Don't assume that the xmlpatterns command is available.

The xmlpatterns command line tool is required when Qt 5 is used.

Task-number: QTCREATORBUG-11768
Change-Id: I7946a35ba66ccfcc44d732a0da2ac836a9640647
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>