tool_metalink: introduce metalink_cleanup() in the internal API

... to release resources allocated at global scope

src/tool_metalink.c

@@ -773,4 +773,8 @@ void clean_metalink(struct Configurable *config)
   config->metalinkfile_last = 0;
 }
 
+void metalink_cleanup(void)
+{
+}
+
 #endif /* USE_METALINK */

src/tool_metalink.h

@@ -144,6 +144,11 @@ int metalink_check_hash(struct Configurable *config,
                         metalinkfile *mlfile,
                         const char *filename);
 
+/*
+ * Release resources allocated at global scope.
+ */
+void metalink_cleanup(void);
+
 #else /* USE_METALINK */
 
 #define count_next_metalink_resource(x)  0

src/tool_operhlp.c

@@ -32,6 +32,11 @@
 #include "tool_operhlp.h"
 #include "tool_version.h"
 
+#ifdef USE_METALINK
+/* import the declaration of metalink_cleanup() */
+#  include "tool_metalink.h"
+#endif
+
 #include "memdebug.h" /* keep this as LAST include */
 
 /*
@@ -215,6 +220,9 @@ void main_free(void)
 {
   curl_global_cleanup();
   convert_cleanup();
+#ifdef USE_METALINK
+  metalink_cleanup();
+#endif
 }
 
 #ifdef CURLDEBUG