I tried the latest Qt 5.5.0 prerelease (http://download.qt.io/snapshots/qt/5.5/5.5.0/2015-06-26_111/qt-opensource-mac-x64-android-ios-5.5.0_2015-06-26_15-55-56-111.dmg) and found that at every compiled files in my projects I get these warnings filing the console :

In file included from ../../../Qt/Qt5.5.0-20150626/5.5/clang_64/lib/QtGui.framework/Headers/QGuiApplication:1:
In file included from ../../../Qt/Qt5.5.0-20150626/5.5/clang_64/lib/QtGui.framework/Headers/qguiapplication.h:37:
In file included from /Users/vlad/Dev/Qt/Qt5.5.0-20150626/5.5/clang_64/lib/QtCore.framework/Headers/qcoreapplication.h:40:
/Users/vlad/Dev/Qt/Qt5.5.0-20150626/5.5/clang_64/lib/QtCore.framework/Headers/qobject.h:108:5: warning: unknown warning group '-Winconsistent-missing-override', ignored [-Wunknown-pragmas]
Q_OBJECT
^
/Users/vlad/Dev/Qt/Qt5.5.0-20150626/5.5/clang_64/lib/QtCore.framework/Headers/qobjectdefs.h:156:5: note: expanded from macro 'Q_OBJECT'
Q_OBJECT_NO_OVERRIDE_WARNING \
^
/Users/vlad/Dev/Qt/Qt5.5.0-20150626/5.5/clang_64/lib/QtCore.framework/Headers/qobjectdefs.h:146:45: note: expanded from macro 'Q_OBJECT_NO_OVERRIDE_WARNING'

1. define Q_OBJECT_NO_OVERRIDE_WARNING QT_WARNING_DISABLE_CLANG("-Winconsistent-missing-override")
   ^
   /Users/vlad/Dev/Qt/Qt5.5.0-20150626/5.5/clang_64/lib/QtCore.framework/Headers/qcompilerdetection.h:1125:49: note: expanded from macro 'QT_WARNING_DISABLE_CLANG'
2. define QT_WARNING_DISABLE_CLANG(text) QT_DO_PRAGMA(clang diagnostic ignored text)
   ^
   /Users/vlad/Dev/Qt/Qt5.5.0-20150626/5.5/clang_64/lib/QtCore.framework/Headers/qcompilerdetection.h:1096:49: note: expanded from macro 'QT_DO_PRAGMA'
   #define QT_DO_PRAGMA(text) _Pragma(#text)
   ^
   <scratch space>:31:27: note: expanded from here
   clang diagnostic ignored "-Winconsistent-missing-override"

Here is the clang version :
$ clang -v
Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.3.0
Thread model: posix

from XCode 6.3.2 (6D2105)
^