Use dl_iterate_phdr() in wxDynamicLibrary::ListLoaded()

This has the advantage of returning libraries in their load order, which
is more useful than the unspecified order that was used before.

It also means that this function now has a chance of working under other
systems such as FreeBSD, which also provides dl_iterate_phdr().

configure.ac

@@ -4839,7 +4839,7 @@ else
                             ])
             ])
 
-            dnl check also for dlerror()
+            dnl check also for some optional functions which we may use
             if test "$HAVE_DL_FUNCS" = 1; then
                 AC_CHECK_FUNCS(dladdr,
                     AC_DEFINE(HAVE_DLADDR),
@@ -4851,6 +4851,8 @@ else
                             ])
                     ]
                 )
+
+                AC_CHECK_FUNCS(dl_iterate_phdr)
             fi
         fi