When building on Windows in the CI environment the Mimer SQL libraries
where not found. The updated script set an environment variable that is
is when building the QtSql Mimer SQL plugin
Fixes: QTBUG-111219
Pick-to: 6.6
Change-Id: Id486a5a3b37d90cd19180f7900456eeae910d1de
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>