Prepare wpiutil for merge into allwpilib.

wpiutil/src/main/native/include/support/mutex.h

@@ -0,0 +1,24 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017-2018 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <mutex>
+
+#include "priority_mutex.h"
+
+namespace wpi {
+
+#ifdef WPI_HAVE_PRIORITY_MUTEX
+using mutex = priority_mutex;
+using recursive_mutex = priority_recursive_mutex;
+#else
+using mutex = ::std::mutex;
+using recursive_mutex = ::std::recursive_mutex;
+#endif
+
+}  // namespace wpi