If qt is first configured without -developer-build, and then
reconfigured with -developer-build, QT_FEATURE_developer_build will be
ON but QT_FEATURE_private_tests remains OFF, and is not reset to ON.
This causes a link failure in Network, because the source files
defining the QNetworkAccessDebugPipeBackendFactory class are only
added if QT_FEATURE_private_tests is ON, which is not the case above,
but the C++ code checks for the QT_INTERNAL_BUILD define which is
defined when -developer-build is ON.
Align the C++ code to check for the private_tests feature.
Pick-to: 6.5 6.6
Task-number: QTBUG-112957
Change-Id: Ib6ed891a84c6b118836497d6ead48019bb1b9052
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
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