Yesterday (3/10/14) when iOS 7.1 was released I also upgraded to Xcode 5.1 and found that my PhoneGap/Cordova project would no longer compile to my iPhone 5s. I also upgrade
Grab the xcode icon and drag it to the bin!
Go here https://developer.apple.com/downloads/index.action?name=Xcode and download 5.0.2 and install.
After installing, run xcode, then try the emulator from terminal.
Worked for me, annoying though!