qmake: make argument validation of built-ins data driven

at the time this patch was conceived, it was meant as an exercise in
getting rid of usages of ProString::toQString(m_tmp). however, this was
meanwhile superseded by use of toQStringView().
but the change itself should have been done a long time ago already, and
there is no harm in going through with it.

on the way, this also unifies and fixes some of the error messages.

Change-Id: I337aff994c508df783df4794c3fa0762d83a691b
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
(cherry picked from qtbase/811d8b82b541e94d154697cb854a29b09ae92a0d)
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>