The feature is present in MSVC 2008 onwards. Fixes warnings when
compiling with 32bit:

main.cpp(97) : warning C4341: 'QtWebKitWidgetsModule' : signed value is out of range for enum constant

Change-Id: I955c5c9f1ed6f1e94c95294e191cc36c5b668391
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>