Force absolute paths with qmake

Force absolute paths with qmake

When generating makefiles, by default qmake tries to use
relative paths if it can replace at most 4 subdirs with "../"
to reach the QTDIR from the project file location.
This maximum can be changed by defining QMAKE_PROJECT_DEPTH, and
setting it to zero forces qmake to always use absolute paths.

This is necessary because the paths for includes and libs are
generated by a temporary project file located in a temporary dir
not corresponding to the real source dir.