vlc_plugin: make header standalone

This can be useful for code that generates static symbols.
We don't need to include `vlc_common.h` anymore.

include/vlc_plugin.h

@@ -24,6 +24,8 @@
 #ifndef LIBVLC_MODULES_MACROS_H
 # define LIBVLC_MODULES_MACROS_H 1
 
+#include <stdint.h>
+
 /**
  * \file
  * This file implements plugin (module) macros used to define a vlc module.