build_wrapper: Add -prefix option for Windows builds

Task-number: QTBUG-31858

Change-Id: Ib81ddea863d6f3ab9a7fe0ee0513645e658d7ff6
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>
build_wrapper: Remove -D QT_EVAL for opensource builds on Windows

Change-Id: I28e5c40782d6789326ede76d4048733ddf023964
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>
build_wrapper: Remove qtconnectivity from the ignore list

qtconnectivity will be part of the Qt 5.2.0 alpha release (at least)

Change-Id: Iacaa5e3d2e80f3518524c0f9192ad9e490726892
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>