coreutils {pr,truncate} --do-not-exist error code is 1 instead of 2

[sylvestre]

example:

$ ./target/debug/coreutils ls --do-not-exist 2> /dev/null; echo $?   
2

but

$ ./target/debug/coreutils pr --do-not-exist 2> /dev/null; echo $?  
1
$ ./target/debug/coreutils cp --do-not-exist 2> /dev/null; echo $?
1
$ ./target/debug/coreutils truncate --do-not-exist 2> /dev/null; echo $?
1

See also
#3331

[tertsdiepraam]

This matches GNU behaviour:

$ cp --does-not-exist 2> /dev/null; echo $?
1

So if we want to change this, it would be an explicit incompatibility with GNU

[sylvestre]

oh, cool.
So, the bug will be closed by my PR then