Rename lock.h to platform.h

And move some more platform specific code there.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/misc.h

@@ -23,7 +23,6 @@
 #include <fstream>
 #include <string>
 
-#include "lock.h"
 #include "types.h"
 
 extern const std::string engine_info(bool to_uci = false);