top-level configure is still verbose in a non-developer build

Calling top-level configure without -developer-build still outputs quite a few messages, even with https://codereview.qt-project.org/c/qt/qtbase/+/398614

Notably all the 'Checking dependencies of submodule' messages, 'Configuring submodule', 'The following packages have been found', and the summary upon reconfiguration even with https://codereview.qt-project.org/c/qt/qtbase/+/415288 applied.

The reason is that we set CMAKE_MESSAGE_LOG_LEVEL in QtSetup within each repo subdirectory scope, whereas the messages above are displayed in the top-level scope, which doesn't have CMAKE_MESSAGE_LOG_LEVEL set in it.