MacOSX-10.10-SDK
Easier Workaround: just change the target in your Qt App .pro file
copy to /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs.
Solves the Qt Creator Warning: "warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk' error: 'TargetConditionals.h' file not found"