stdio-common: Fix C23-ism in formatted output specifier tests [BZ #32360]

Nameless function parameters have only been added to ISO C with the C23
revision of the language standard.  Give names to the unused parameters
of the stub 'dladdr' implementation then so as to make compilation happy
with the earlier language definitions, fixing errors such as:

tst-printf-format-skeleton.c:374:9: error: parameter name omitted
  374 | dladdr (const void *, Dl_info *)

reported by older compilers.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

stdio-common/tst-printf-format-skeleton.c

@@ -371,7 +371,7 @@ do_test (int argc, char *argv[])
 /* Interpose 'dladdr' with a stub to speed up malloc tracing.  */
 
 int
-dladdr (const void *, Dl_info *)
+dladdr (const void *addr, Dl_info *info)
 {
   return 0;
 }