libsemanage: add extern prototype for legacy function

    modules.c:171:13: warning: no previous prototype for ‘semanage_module_get_version’ [-Wmissing-prototypes]
      171 | const char *semanage_module_get_version(semanage_module_info_t * modinfo
          |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
diff --git a/libsemanage/src/modules.c b/libsemanage/src/modules.c
index b6dd456..c98df4d 100644
--- a/libsemanage/src/modules.c
+++ b/libsemanage/src/modules.c
@@ -168,6 +168,7 @@
 /* Legacy function that remains to preserve ABI
  * compatibility.
  */
+extern const char *semanage_module_get_version(semanage_module_info_t *);
 const char *semanage_module_get_version(semanage_module_info_t * modinfo
 				__attribute__ ((unused)))
 {