deps: backport 85adf43e from libuv upstream

Original commit message:

    unix: consolidate rwlock tryrdlock trywrlock errors

    Fold EAGAIN and EBUSY into EBUSY. This makes it consistent across all
    Unix platforms and Windows.

    Refs: https://github.com/libuv/libuv/pull/525
    PR-URL: https://github.com/libuv/libuv/pull/535
    Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

PR-URL: https://github.com/nodejs/node-private/pull/54
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>

deps/uv/src/unix/thread.c

@@ -162,10 +162,13 @@ int uv_rwlock_tryrdlock(uv_rwlock_t* rwlock) {
   int err;
 
   err = pthread_rwlock_tryrdlock(rwlock);
-  if (err && err != EBUSY && err != EAGAIN)
+  if (err) {
-    abort();
+    if (err != EBUSY && err != EAGAIN)
+      abort();
+    return -EBUSY;
+  }
 
-  return -err;
+  return 0;
 }
 
 
@@ -185,10 +188,13 @@ int uv_rwlock_trywrlock(uv_rwlock_t* rwlock) {
   int err;
 
   err = pthread_rwlock_trywrlock(rwlock);
-  if (err && err != EBUSY && err != EAGAIN)
+  if (err) {
-    abort();
+    if (err != EBUSY && err != EAGAIN)
+      abort();
+    return -EBUSY;
+  }
 
-  return -err;
+  return 0;
 }