use memcmp instead of strncmp in C++ scanner
use memcmp instead of strncmp in C++ scanner

We already know the actual string length, so there is no point
in having the function figure it out itself.

Change-Id: I34303ba07e46c634dac42228479ed59ae2966592
Reviewed-by: Oswald Buddenhagen <6a8868beda3e139b5ac22b2534a23d3e6ba81819@digia.com>

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