gdb: cast return value of std::unique_ptr::release to void

My editor shows warnings like:

     value.c:2784: warning: The value returned by this function should be used
     value.c:2784: note: cast the expression to void to silence this warning [bugprone-unused-return-value]

These warnings come from clangd, so ultimately from one of the clang
static analyzers (probably clang-tidy).

Silence these warnings by casting to void.  Add a comment to explain
why this unusual thing is done.

Change-Id: I58323959c0baf9f1b20a8d596e4c58dc77c6809a
Approved-By: Tom Tromey <[email protected]>

Author: simark

gdb/value.c

@@ -2347,9 +2347,12 @@ add_internal_function (gdb::unique_xmalloc_ptr<char> &&name,
 {
   struct cmd_list_element *cmd
     = do_add_internal_function (name.get (), doc.get (), handler, cookie);
-  doc.release ();
+
+  /* Manually transfer the ownership of the doc and name strings to CMD by
+     setting the appropriate flags.  */
+  (void) doc.release ();
   cmd->doc_allocated = 1;
-  name.release ();
+  (void) name.release ();
   cmd->name_allocated = 1;
 }