setupmtplatforms: Make qmake output parsing more robust.
setupmtplatforms: Make qmake output parsing more robust.

Try to filter output that does not come from us, e.g. warnings.

Change-Id: I558460e2113bf8d9e6b82564f9e1b149855ca5e7
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@nokia.com>

gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,villytiger/qbs,qt-labs/qbs,villytiger/qbs,qtproject/qt-labs-qbs,villytiger/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,qt-labs/qbs,Distrotech/qbs,villytiger/qbs,qtproject/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,villytiger/qbs,Distrotech/qbs,qt-labs/qbs,qt-labs/qbs,villytiger/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs