'stdio.h' file not found, but I have this file at /usr/include/stdio.h
The root cause of the error message is from the warning message:


  clang: warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk'


By checking SDKs directory:

$ cd /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/
$ ls
MacOSX.sdk/      MacOSX10.13.sdk


So, to workaround the problem, it's either re-install xcode suggested by @Mark or create a symbolic link like the following:

$ sudo ln -s MacOSX.sdk/ MacOSX10.14.sdk