cleanup: include stdlib.h instead of defining NULL in PRCommon.h

src/PRCommon.h

@@ -37,6 +37,4 @@
 void PRLog(PRLogLevel level, const char *format, ...);
 void PRSetLastErrorText(const char *format, ...);
 
-#define NULL 0
-
 #endif /* PINPROC_PRCOMMON_H */

src/PRHardware.cpp

@@ -28,7 +28,7 @@
  *  libpinproc
  */
 
-
+#include <stdlib.h>
 #include "PRHardware.h"
 #include "PRCommon.h"