test: use error code mapping in place of raw errno

Refs: https://github.com/nodejs/node/pull/38159#discussion_r610288214

PR-URL: https://github.com/nodejs/node/pull/38675
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

test/parallel/test-fs-read-type.js

@@ -117,7 +117,7 @@ fs.read(fd,
         common.mustCall((err) => {
           if (err) {
             if (common.isIBMi)
-              assert.strictEqual(err.errno, -127);
+              assert.strictEqual(err.code, 'EOVERFLOW');
             else
               assert.strictEqual(err.code, 'EFBIG');
           }
@@ -238,6 +238,6 @@ try {
   // On systems where max file size is below 2^53-1, we'd expect a EFBIG error.
   // This is not using `assert.throws` because the above call should not raise
   // any error on systems that allows file of that size.
-  if (err.code !== 'EFBIG' && !(common.isIBMi && err.errno === -127))
+  if (err.code !== 'EFBIG' && !(common.isIBMi && err.code === 'EOVERFLOW'))
     throw err;
 }