title: Linux QT GCC OpenGL GLEW - add parameters to compiler
body: <p>I want to create example GLFW file in C++.
  When I type in Terminal <code>gcc FILENAME.cpp -lGL -lGLEW -lglfw</code> everything is OK,
  but...
  When I want to use CTRL+B to build my file in Qt Creator,
  I see error <code>undefined reference to glfwInit</code>. I know I must add flags <code>-lGL -lGLEW -lglfw</code>, I tried to add <code>QMAKE_CXXFLAGS += -lGL -lGLEW -lglfw</code> in my <code>pro</code> file, but it does not work.</p>
  
  <p>What is correct way to do this?</p>