Common: Move header guards over to pragma once

Also replaced C headers with the C++ equivalent ones

src/common/std_mutex.h

@@ -1,6 +1,4 @@
-
-#ifndef MUTEX_H_
-#define MUTEX_H_
+#pragma once
 
 #define GCC_VER(x,y,z)    ((x) * 10000 + (y) * 100 + (z))
 #define GCC_VERSION GCC_VER(__GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__)
@@ -362,4 +360,3 @@ void swap(unique_lock<Mutex>& x, unique_lock<Mutex>& y)
 }
 
 #endif
-#endif