We forwarded the compiler path to the EP but not the flags that might
have been set via the CXX environment variable.
Make sure to also forward the flags.
Task-number: QTBUG-90820
Task-number: QTBUG-96232
Change-Id: I0fbf9b595f7885014b1f09d158db52e56a3d5243
Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>
(cherry picked from commit 7fb25609a41ab9cc20ddd62e90f30c0536502aef)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
53cdf7525e