Setting QT_ARCH when empty is a workaround for a missing qconfig.pri,
since it hasn't been written yet by configure. As qconfig.pri is
loaded by the generic qt_config.prf, putting our workaround in
our own wrapper for qt_config makes sense, as it keeps the logic
close to where the original QT_ARCH is resolved.
Change-Id: I49ffc21cf5dea5ca5b6254ca8084a4dcdc359a72
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
