Optionally run qmake on every project rebuild

After pulling in most changes affecting the project definition I found necessary to do a manual "run qmake" before a full rebuilt or risk getting unexpected results.

I think having a build option to automatically run qmake before full rebuilds would make this workflow a lot more developer friendly.

PS. Besides the fact that a qmake run is neccesary in most cases, even with multiple subprojects (10+) qmake takes a relatively miniscule time (few seconds) compared to the actual rebuild.