Don't use perror when errno has not been set

For non-syscall-related error messages, use the classical fprintf to
print an informative error message.

Signed-off-by: Celelibi <celelibi@gmail.com>
Use a separated function for system error handling

This function, system_error, basically just calls perror and exit. It
allows to emergency quit when a syscall return an error with only one
line of code.

Signed-off-by: Celelibi <celelibi@gmail.com>
Typo in comments

s/clic/clique/

Signed-off-by: Celelibi <celelibi@gmail.com>
Converted end-of-line to unix-style

Because git doesn't like the DOS style.

Signed-off-by: Celelibi <celelibi@gmail.com>