Fix race condition on QQmlEnginePrivate::qml_debugging_enabled

C++11 allows static dynamic initialization from different TUs to
happen concurrently, which means the QQmlDebuggingEnabler ctor must be
re-entrant and synchronized with other users of qml_debugging_enabled.

Thankfully, this is just a flag, so the fix is to simply make it
atomic<> and use relaxed loads and stores on it.

Manual conflict resolutions:
  - dropped the Q_CONSTINIT (doesn't exist in 5.15)
  - actual line conflicts in src/qml/qml/qqmlengine_p.h

Change-Id: I0305ab55be86a0e286016a3d1d97ee9bc0e28070
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit 0434e54b55d9a31c3b5331856bab639b7149058c)
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

0 files changed, 0 insertions, 0 deletions