Method 1
This kind of error will appear every time you upgrade Xcode
so you can remove cache file in qt before you build or just remove when you get the error
rm {your target build folder}/.qmake.stash
or
rm {your project folder}/.qmake.stash
if you don't know where to find .qmake.stash, try
find ~ -name .qmake.stash
Method 2
Not recommend because you could get build error when you use Xcdoe APP
iphoneOS
cd /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/
sudo ln -s iPhoneOS.sdk iPhoneOS{version}.sdk
iPhoneSimulator
cd /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/
sudo ln -s iPhoneSimulator.sdk iPhoneSimulator{version}.sdk
ls /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs.MacOSX10.9.sdkis likely listed, and it should be used rather thanMacOSX10.8.sdk.