Build improvements

Do not try to compile headers files, this fails on some systems.

Disable C++11 compat warnings on non-linux unix based systems.

Change-Id: I02457db61a61068261d2717eee74f58bdf496f58
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Update configure warnings

The configure warnings issued by Qt WebKit are slightly outdated. This
updates then to be more accurate to what caused the failure and where
it can be fixes.

Change-Id: Iec41c20c86787dd95c8cb209604747587e7931bc
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Use global Qt configuration for libudev

Only build WebKit with libudev dependency if Qt was configured with libudev.

Task-number: QTBUG-34176
Change-Id: Iaabb2401e2dc4a91d46a5e4f759546e0de278a08
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>