If debug_and_release is set then QtWebEngineProcess should be built in
release mode as it is a separate process and when it is deployed later it
will be in the right mode already.

Change-Id: I377baa20f01b70db91a7a1cec5f1014b44780546
Reviewed-by: Michael Brüning <michael.bruning@theqtcompany.com>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>