QMAKESPEC=macx-xcode generates an Xcode project that wont compile

Mac OS X with latest Xcode version 4.6.2. Any project, including Qt examples.

Set QMAKESPEC=macx-g++, then run qmake and make -> works fine

Set QMAKESPEC=macx-xcode, then run qmake, open the XCode project, and 'build' -> the compiler fails with the following errors...

cc1plus: error: unrecognized command line option "-Wno-exit-time-destructors"
cc1plus: error: unrecognized command line option "-Wno-constant-conversion"
cc1plus: error: unrecognized command line option "-Wno-int-conversion"
cc1plus: error: unrecognized command line option "-Wno-enum-conversion"
cc1plus: error: unrecognized command line option "-Wno-c++11-extensions"
cc1plus: error: unrecognized command line option "-Wno-sign-conversion"
cc1plus: error: unrecognized command line option "-fserialize-diagnostics"
Command /Applications/Xcode.app/Contents/Developer/usr/bin/g++ failed with exit code 1

Here's the compile command line that Xcode generated...

/Applications/Xcode.app/Contents/Developer/usr/bin/g++ -x c++ -arch x86_64 -fmessage-length=0 -Wno-trigraphs -fpascal-strings -O0 -Wno-missing-field-initializers -Wno-missing-prototypes -Wno-return-type -Wno-non-virtual-dtor -Wno-overloaded-virtual -Wno-exit-time-destructors -Wformat -Wno-missing-braces -Wparentheses -Wswitch -Wno-unused-function -Wno-unused-label -Wno-unused-parameter -Wno-unused-variable -Wunused-value -Wno-empty-body -Wno-uninitialized -Wno-unknown-pragmas -Wno-shadow -Wno-four-char-constants -Wno-conversion -Wno-constant-conversion -Wno-int-conversion -Wno-enum-conversion -Wno-shorten-64-to-32 -Wno-newline-eof -Wno-c++11-extensions -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk -fasm-blocks -fstrict-aliasing -Wdeprecated-declarations -Winvalid-offsetof -mmacosx-version-min=10.6 -g -fvisibility=hidden -fvisibility-inlines-hidden -Wno-sign-conversion -I/Users/axograph/qt5/qtbase/examples/widgets/mainwindows/sdi/.obj/debug-shared/sdi.build/Debug/sdi.build/sdi.hmap -I/Users/axograph/qt5/qtbase/examples/widgets/mainwindows/sdi/Debug/include -I../../../../include -I../../../../include/QtWidgets -I../../../../lib/QtWidgets.framework/Versions/5/Headers -I../../../../include/QtGui -I../../../../lib/QtGui.framework/Versions/5/Headers -I../../../../include/QtCore -I../../../../lib/QtCore.framework/Versions/5/Headers -I.moc/debug-shared -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk/System/Library/Frameworks/OpenGL.framework/Versions/A/Headers -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk/System/Library/Frameworks/AGL.framework/Headers -I/usr/local/include -I/System/Library/Frameworks/CarbonCore.framework/Headers -I../../../../mkspecs/macx-xcode -I/Users/axograph/qt5/qtbase/examples/widgets/mainwindows/sdi/.obj/debug-shared/sdi.build/Debug/sdi.build/DerivedSources/x86_64 -I/Users/axograph/qt5/qtbase/examples/widgets/mainwindows/sdi/.obj/debug-shared/sdi.build/Debug/sdi.build/DerivedSources -F/Users/axograph/qt5/qtbase/examples/widgets/mainwindows/sdi/Debug -F/Users/axograph/qt5/qtbase/lib -pipe -g -gdwarf-2 -fno-exceptions -Wall -W -fPIE -DQT_NO_LIBUDEV -DQT_NO_EVDEV -DQT_NO_XCB -DQT_NO_XKBCOMMON -DQT_NO_EXCEPTIONS -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -MMD -MT dependencies -MF /Users/axograph/qt5/qtbase/examples/widgets/mainwindows/sdi/.obj/debug-shared/sdi.build/Debug/sdi.build/Objects-normal/x86_64/qrc_sdi.d --serialize-diagnostics /Users/axograph/qt5/qtbase/examples/widgets/mainwindows/sdi/.obj/debug-shared/sdi.build/Debug/sdi.build/Objects-normal/x86_64/qrc_sdi.dia -c .rcc/debug-shared/qrc_sdi.cpp -o /Users/axograph/qt5/qtbase/examples/widgets/mainwindows/sdi/.obj/debug-shared/sdi.build/Debug/sdi.build/Objects-normal/x86_64/qrc_sdi.o