CMake error no CMAKE_C_COMPILER could be found using Xcode and GLFW
Did you install Xcode and Xcode Commandline Tools?
xcode-select --installIf you have Xcode Commandline Tools installed, you should no longer be receiving the xcrun is missing error.
How did you install Cmake? Once you have ensured that Xcode Commandline Tools is installed, please completely remove Cmake from your system and reinstall it. You have a screwed up configuration. There are ways to debug and fix it without a clean install, but since you are new to this, it will be the easiest and lest frustrating way.
Failing that if you do have Xcode Commandline Tools installed, hstdt suggested trying this:
sudo xcode-select --reset