Cannot compile QtCreator master using released Qt5.3.2 on OSX using Xcode 6

Steps to reproduce:

• have Xcode 6 and the released Qt5.3.2 installed
• clone qt-creator repo including submodule
• try to run qmake on qtcreator.pro, I've used

  ~/Qt5.3.2/5.3/clang_64/bin/qmake CONFIG+=debug ../qt-creator
  

  from the build directory

Expected result:

• Makefile is created, compile can be started

Current result:

• qmake fails with an error stating

  Project ERROR: Could not resolve SDK path for 'macosx10.8'
  

• you have to explicitly call qmake by passing QMAKE_MAC_SDK=macosx to make it work