Make use of -lppapi explicit to allow for correct library order.

native_client_sdk/src/libraries/pthread/pthread.c

+/* Copyright (c) 2012 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include <windows.h>
+#include <errno.h>
+#include "pthread.h"
+
+int pthread_mutex_init(pthread_mutex_t* m, void* traits) {
+  *m = (int) CreateMutex(NULL, 0, NULL);
+  return 0;
+}
+
+int pthread_mutex_destroy(pthread_mutex_t* m) {
+  CloseHandle((HANDLE) *m);
+  return 0;
+}
+
+int pthread_mutex_lock(pthread_mutex_t* m) {
+  if (WaitForSingleObject((HANDLE) *m, INFINITE) == WAIT_OBJECT_0)
+    return 0;
+
+  return EINVAL;
+}
+
+int pthread_mutex_unlock(pthread_mutex_t* m) {
+  if (ReleaseMutex((HANDLE) *m)) return 0;
+
+  return EINVAL;
+}
+
+int pthread_mutex_trylock(pthread_mutex_t* m) {
+  int val = WaitForSingleObject((HANDLE) *m, 0);
+  
+  if (val == WAIT_OBJECT_0) return 0;
+
+  if (val == WAIT_TIMEOUT) {
+    errno = EBUSY;
+  } else {
+    errno = EINVAL;
+  }
+  return -1;
+}