configure: fixed qconfig.h symlink warnings

configure: fixed qconfig.h symlink warnings

configure was unconditionally attempting to create two symlinks to
qconfig.h: include/Qt/qconfig.h, and include/QtCore/qconfig.h.

include/Qt doesn't exist any more, so this would always cause a
"No such file or directory" warning.  Remove that one.

include/QtCore/qconfig.h is usually created by syncqt now, so this would
cause a "File exists" warning.  Make that one conditional.

Change-Id: I8c6244dcbcf9765444f0d5c40c91a0ca192ecbcb
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>