[Development] qmake command line assignments are not considered by config.tests

[Roland Winklmeier]

Dear Qt devs,

I addressed the question below first to the interest list. But since
nobody replied, I did some investigations and found out this behavior
is caused by the macro qtCompileTest defined in
qtbase/mkspecs/features/configure.prf.

I also found a codereview similar to what I had planned to submit (
https://codereview.qt-project.org/#/c/96521/ ) but it was abandoned
with the explanation the tests should be self-contained and I agree
with that. However, I'm still missing a feature to add custom include
and linker paths. Otherwise qtCompileTest is just not usable on
Windows.

Cheers R.