shared: include <stdlib.h> in "nm-macros-internal.h"

"nm-macros-internal.h" uses free() for the "nm_auto_free"
macro. Thus, as long as that code is there, we anyway must
include <stdlib.h> along the line.

Do it in "nm-macros-internal.h" to make the header self-contained.

shared/nm-macros-internal.h

@@ -22,6 +22,8 @@
 #ifndef __NM_MACROS_INTERNAL_H__
 #define __NM_MACROS_INTERNAL_H__
 
+#include <stdlib.h>
+
 /********************************************************/
 
 #define nm_auto(fcn) __attribute ((cleanup(fcn)))