Well I downloaded the wrong source ("Library Source with split build system"). OK but now I can't get it work because of ld:
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QWidget::accessibleDescription() const'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QString::isRightToLeft() const'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QVectorData::reallocate(QVectorData*, int, int, int)'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QWidget::accessibleName() const'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QDesktopWidget::availableGeometry(QWidget const*) const'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QListData::detach_grow(int*, int)'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QListData::detach(int)'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QWidget::setAccessibleDescription(QString const&)'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QVectorData::free(QVectorData*, int)'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QDesktopWidget::screenGeometry(QWidget const*) const'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `qBadAlloc()'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QWidget::setAccessibleName(QString const&)'
D:\Programme\Lazarus\fpc\2.5.1\libcross\arm\QT\/libQt4Pas.so: undefined reference to `QVectorData::allocate(int, int)'