Accomodate for different status message on Windows

Alternatively we could change the error message to
only include take the status code from the os by
using

output.status.code().unwrap() in preprocess/cmd.rs
where this error message is generated.

In that case we could have the exact same error
message on all the OS-es.

Author: szabgab

tests/custom_preprocessors.rs

@@ -44,9 +44,16 @@ fn ask_the_preprocessor_to_blow_up() {
 
     assert!(got.is_err());
     let error_message = got.err().unwrap().to_string();
+    let status = if cfg!(windows) {
+        "exit code: 1"
+    } else {
+        "exit status: 1"
+    };
     assert_eq!(
         error_message,
-        r#"The "nop-preprocessor" preprocessor exited unsuccessfully with exit status: 1 status"#
+        format!(
+            r#"The "nop-preprocessor" preprocessor exited unsuccessfully with {status} status"#
+        )
     );
 }