cmake _GLFW_HAS_GLXGETPROCADDRESSEXT examples

slicol/Games101-Homework-Win Assignment8/CGL/deps/glfw/CMakeLists.txt :398 

check_function_exists(glXGetProcAddressEXT _GLFW_HAS_GLXGETPROCADDRESSEXT)

openglsuperbible/sb7code extern/glfw-3.0.4/CMakeLists.txt :279 

check_function_exists(glXGetProcAddressEXT _GLFW_HAS_GLXGETPROCADDRESSEXT)