外部库在Qt Creator中抛出未定义的引用错误

I have some problems with using an external library/SDK. I am using Qt Creator under Ubuntu with the Oculus Rift SDK. The Oculus Rift SDK consists of a platform dependent lib file and some c++ source code. Note that I highly doubt my problem is in any way specific to the Oculus SDK or Xinerama.I have some problems with using an external lib