[webkit-qt] Treat warnings as errors by QtWebKit

[Osztrogonac Csaba]

Dear WebKit Community,

in the past weeks we have worked on fixing warnings of QtWebKit. Now it's
time to treat warnings as errors to warrant better code quality. First we
enabled -Werror on x86/Linux platforms, and in the near future we are going
to enable it for other Qt platforms. (ARM/Linux, x86/Windows, ...)

 From now any warning will break "Qt Linux Release", "Qt Linux Release minimal"
buildbots and the Qt EWS bot. Please take notice of their redness.

FYI: master bug of this topic - https://bugs.webkit.org/show_bug.cgi?id=43191

With best regards:
Csaba Osztrogonác (ossy on #webkit, ossy {at} webkit {dot} org)
University of Szeged
http://webkit.sed.hu