Removed dependencies on pthread from frcsim.

Because we want to be able to compile/run wpilibC++Sim on
windows, we would prefer not to require a windows version
of pthread. This commit moves from pthread constructs to
standard library constructs.

Change-Id: I12392a8910189537dd067afdf017e4994d570a66

hal/include/HAL/cpp/priority_mutex.h

@@ -1,10 +1,17 @@
 #pragma once
 
-#include <pthread.h>
-
 // Allows usage with std::unique_lock without including <mutex> separately
 #include <mutex>
 
+#ifdef FRC_SIMULATOR
+// We do not want to use pthreads if in the simulator; however, in the
+// simulator, we do not care about priority inversion.
+typedef ::std::mutex priority_mutex;
+typedef ::std::recursive_mutex priority_recursive_mutex;
+#else // Covers rest of file.
+
+#include <pthread.h>
+
 class priority_recursive_mutex {
  public:
   typedef pthread_mutex_t *native_handle_type;
@@ -65,3 +72,5 @@ class priority_mutex {
       {0, 0, 0, 0x20, 0, {0}}};
 #endif
 };
+
+#endif  // FRC_SIMULATOR