deps: backport bd1777fd from libuv upstream

Original commit message:

    unix, win: consolidate mutex trylock errors

    Fold EAGAIN into EBUSY, and make it the only acceptable error.

    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

@@ -124,14 +124,14 @@ void uv_mutex_lock(uv_mutex_t* mutex) {
 int uv_mutex_trylock(uv_mutex_t* mutex) {
   int err;
 
-  /* FIXME(bnoordhuis) EAGAIN means recursive lock limit reached. Arguably
-   * a bug, should probably abort rather than return -EAGAIN.
-   */
   err = pthread_mutex_trylock(mutex);
-  if (err && err != EBUSY && err != EAGAIN)
-    abort();
+  if (err) {
+    if (err != EBUSY && err != EAGAIN)
+      abort();
+    return -EBUSY;
+  }
 
-  return -err;
+  return 0;
 }
 
 

deps/uv/src/win/thread.c

@@ -211,7 +211,7 @@ int uv_mutex_trylock(uv_mutex_t* mutex) {
   if (TryEnterCriticalSection(mutex))
     return 0;
   else
-    return UV_EAGAIN;
+    return UV_EBUSY;
 }