It checks whether the symbols are defined in an included header file. The `compare` and `generic_fizz_buzz` are not defined in any header files that are include

It checks whether the symbols are defined in an included header file. The `compare` and `generic_fizz_buzz` are not defined in any header files that are included so they are obfuscated. One example of this is `printf`, it would be obfuscated if it wasn't for the fact that it's defined in `stdio.h`. You can try removing that `include` and you'll see that it is then renamed. The name it creates for each identifier is the md5 of the identifier.