Add confirm_conf option

If the confirm_conf option is set, when the program starts, each of
the four malloc_conf strings will be printed, and each option will
be printed when being set.

include/jemalloc/internal/jemalloc_internal_externs.h

@@ -10,6 +10,7 @@ extern bool malloc_slow;
 /* Run-time options. */
 extern bool opt_abort;
 extern bool opt_abort_conf;
+extern bool opt_confirm_conf;
 extern const char *opt_junk;
 extern bool opt_junk_alloc;
 extern bool opt_junk_free;