Remove mark maybe from imemo_tmpbuf

If `xcalloc` is used instead of `xmalloc` for `imemo_tmpbuf`, then
calling `rb_gc_mark_locations` on the internals of the `imemo_tmpbuf` is
no longer necessary.

The main goal is to avoid mark maybe / mark and pin on objects where it
isn't actually required. This is required for MMTk moving immix
implementation, however it's more efficient in the standard GC as well
to avoid pinning unnecessarily. Otherwise objects are pinned and not
compacted.

[link issue]

Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org>

Author: eileencodes

imemo.c

@@ -68,7 +68,7 @@ rb_alloc_tmp_buffer_with_count(volatile VALUE *store, size_t size, size_t cnt)
      * get rid of potential memory leak */
     tmpbuf = rb_imemo_tmpbuf_new();
     *store = (VALUE)tmpbuf;
-    ptr = ruby_xmalloc(size);
+    ptr = ruby_xcalloc(size, sizeof(char));
     tmpbuf->ptr = ptr;
     tmpbuf->cnt = cnt;
 
@@ -408,14 +408,6 @@ rb_imemo_mark_and_move(VALUE obj, bool reference_updating)
         break;
       }
       case imemo_tmpbuf: {
-        const rb_imemo_tmpbuf_t *m = (const rb_imemo_tmpbuf_t *)obj;
-
-        if (!reference_updating) {
-            do {
-                rb_gc_mark_locations(m->ptr, m->ptr + m->cnt);
-            } while ((m = m->next) != NULL);
-        }
-
         break;
       }
       default: