When a qt.conf was present, QT_HOST_* variables got a wrong default
value. For example, QT_HOST_BINS would end with /bin/bin.
We must not provide the defaults via QSettings::value(_, defaultValue).
The assignment of the default value is done in
QMakeLibraryInfo::rawLocation() separately after retrieving the value.
This amends commit 04ec14105e.
Pick-to: 6.3
Fixes: QTBUG-99656
Change-Id: I43431664e93ab40417a5432b03e7eb38ae21bad8
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
9d15854138