Fix profile setup for mingw-qt4.
Fix profile setup for mingw-qt4.

When extracting the mkspec name, we must not capture the trailing
"/qmake.conf" in our regular expression.

Change-Id: I0bca572ca173e1300ced6d5753d4140a12e33a6e
Reviewed-by: Oswald Buddenhagen <6a8868beda3e139b5ac22b2534a23d3e6ba81819@theqtcompany.com>

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